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