you can get (4) 8" strips from a yard of fabric; (leaving 4")...you can get (5) 8" squares from the width of your 8" strips (based on 40" of usable fabric.) so you can get (20) 8" squares from each yard of fabric. if you sew 10 of those squares together you will have a row 70" x 8"...
one of the things about quilting...there is always alot of math!