Joey painted his four square walls in his bedroom with one can of paint. if the paint can covers 256 ft², how wide is each wall?

Well if the paint covers 256 sq ft, all you have to do is divide that by 4 (because you have 4 square walls) and you get an answer of 64 sq ft.  So each wall would be 8ft wide, and 8ft tall. 

Assuming each wall is same area

aera of 1 wall=totalarea/number of walls=256/4=64ft

square is side^2

side^2=64
sqrt both sides
side=8

each wall is 8ft wide