Unit 3 Instructions
Units 1 and 2 were assemblies of elongated rectangles into columns or vertical rows. Unit 3 is a different approach to the same concept... the assembly of variously proportioned rectangles into a "sub-assembly" rectangle.. In width, it is designed to be the equal of a specific number of vertical columns or rows... in this case, four. In other words, it must end up filling a horizontal space equal to the horizontal dimension of the four vertical rows we have made. They are nominally 6" wide each, or a total of 24" (disregarding seam allowances), so our new Unit 3 rectangle will be nominally 24" wide in total. That will make our quilt top 48", as planned. Don't you just love it when a plan comes together?
For Unit 3 you are going to have to cut one piece that is very large and will require some careful cutting technique. I'll give you some specifics when it's time to cut that one.
I continue t have a lot of trouble with my yellows and oranges. In this unit there are two oranges... a lighter one and a darker one. The lighter one was supposed to be the "yellow orange", but the color I had for that just doesn't work for me. Once again, this isn't critical. If you like the shade you got for that color designation, fine.
You will need five pieces for Unit 3. Cut them to these dimensions, seam allowances included. Measure and cut carefully. If this piece doesn't fit, you will have a real problem and end up doing a lot of frogging... ask me how I know!
Here is the list of pieces you will need for Unit 3:
Lilac 6.5" x 8.5"
Dark Orange 12.5" x 8.5"
Either Green (I used my Moss Green) 6.5" x 13.5"
Light Orange (Yellow Orange from the color chart) 6.5" x 12.5"
Cream 17.5" x 18.5" (Wait and cut this piece last, when we get to it. I will show you a good way to handle cutting a piece this large)
Sub-1 of Unit 3 will consist of the 6.5" x 13.5" Green piece and the 6.5" x 12.5" Light Orange piece, joined as shown:
Note that this piece is 6.5" wide, the same as the previous vertical rows you made. Its height should be 25.5".
Sub-2 of Unit 3 will consist of the 12.5" x 8.5" Dark Orange and the 6.5" x 8.5" Lilac pieces, joined as shown:

Note that this piece ends up being 18 1/2" wide... the equivalent of three of the vertical rows, plus the always necessary seam allowances.
Sub-3 of Unit 3 is one piece, the large Cream rectangle, 17.5" x 18.5". You can measure and cut this piece any way you want... marking with a long ruler and using scissors, or whatever. I like to rely on roller cutting with plastic guides, but I don't have a 24" square (Do they make them?) Anyway, I combined my long 6" x 24" guide and my 15" square guide to provide the measurements I needed... like so:

Here I have laid out the piece of Cream fabric, put my 15" square on one side, added my 8 1/2" x 24" guide to provide the actual full length cutting edge, combined the measurements to get what I needed, and then cut on the long edge.

Here I have turned the cutting guides on the previously cut piece of Cream fabric and set them up to provide the other dimension needed, and will make the cut accordingly.
How you cut this piece isn't really critical, as long as you cut it well! The corners must be square, and it must end up measuring 17.5" x 18.5". Note that 18.5" just happens to be the width of the combined Lilac and Orange pieces you just finished. Funny how that worked out...
Now make what I will call Sub-4 of Unit 3 by sewing the 18.5" edge of the Cream rectangle to the bottom of Sub-2 as shown:

Hopefully, your measurements came out right and these pieces fit together as shown. The finished measurement should be 18.5" wide x 25.5" high.
Finally, we complete the assembly. Sub-1 will be joined to the left edge of Sub-4 as shown:

Since the vertical dimension of Sub-1 was 25.5" and the vertical demension of Sub-4 was also 25.5", they should match up perfectly. The horizontal dimension of this completed unit should be 24.5"... the equivalent of four 6" vertical rows, plus seam allowance.
That's it for Unit 3.
Link to Instructions for Unit 4