I think we're agreed that if you're just sewing jelly roll strips together you need 7 strips to give you an unfinished width of 14.5" But there I have to disagree with the math from above. You need a total of 9x7=63 strips (not 126), but they are only 14.5" wide. Each jelly roll strip will give you two of these strips, so you only need 32 strips. You will be using only 14.5" from one of the strips. And as others said, you could use fewer if you piece the remaining fabric from each WOF strip.