Take into account that the number of feet required to build the fence is determined by the perimeter of the rectangular playground. Consider that the perimeter of a rectangle is given by:
P =2w + 2l
where,
w: width = 90ft
l: length = 50ft
Replace the previous values of w and l into the expression for P and simplify:
P = 2(90ft) + 2(50ft)
P = 180ft + 100ft
P = 280ft
Hence, 280ft are required to buil a fence around the rectangular playground.
