2 plus 2 plus 3.5 equals 7.5
for 6.5 you need
2 plus 2 plus 2.5 BUT when you put those together it will NOT EQUAL 6.5 because of your two 1/4 inch seam allowances SO
you need 2 plus 2 plus 3 equals 7 minus 1/2 inch for 2 seams equals the same 6 1/2 as the other block.