Not sure about the directions but if you mean to crosscut/subcut those
(4) 2 1/2 x 42" strips into (8) 2 1/2 X 10 1/2" rectangles and
(8) 2 1/2 X 6 1/2" rectangles. Then, yes you will have enough.
First you cut (4) 2 1/2 x 41". Then you take each strip and cut
(2) 2 1/2" x 10 1/2" + (2) 2 1/2" x 6 1/2"
That will give you 8 strips of 10 1/2" and 8 strips of 6 1/2" long.
Hope this is clear.
You can draw in on square paper first. It's called a cutting plan.