Question

you are making posters 2ft by 4ft. how many square feet of material will you need for eight posters

Answer 1

You can approach this at least two ways.

First, one poster is 2 * 4 = 8 sq. ft.
Eight posters is 8 * 8 = 64 sq. ft.

Or -- you can figure that you need 16 feet of 4 ft. wide material.

4 * 16 = 64 sq. ft.