Get out your rotary cutter, and away we go!
First, you will make some half square triangles that will finish at 3½” square. If you are like me and never seem to get them to come out at the perfect size, try this trick - cut your squares a bit larger; sew, press and then trim to size. If you are always spot on, you can do these the “correct” way (“correct” according to the quilt police) and cut your squares at 3-7/8”. P.S. No quilt police allowed here, so don’t worry about how you make your half square triangles. There are lots of methods out there for you to choose from.
From A and B cut a WOF of each, I cut them at a bit generous 4-1/8” wide. From these strips cut 6 of A and 6 of B at the 4-1/8” mark, ending up with 6 each of A and B, 4-1/8” square. Set the leftover strips aside for later. Or cut at 3-7/8” if you are doing them the so-called “correct” way. Place right sides together, mark a diagonal from corner to corner, sew ¼” away from each side of the line, cut along the drawn line, press. Trim as needed to 3-½” square. There will be 12 of these half square triangle blocks.
If you need instructions on marking and sewing, see the simple diagram below. More detailed instructions can be found on the internet.
From A and C cut three squares of each fabric measuring 4” square. Again, I am having you cut the fabric a bit larger, and it will be trimmed at a later date. Cut each piece from corner to corner, to make 4 pieces of each fabric. Using the picture as a guide, sew two short sides of A and C together, making 12 triangular pieces. Start stitching from the long straight edge, sewing toward the point. Always keep the A and C fabrics in the same position so the triangles are identical. You will have 12 of the small triangular pieces.
this is a copy/paste with the corrections