The formula for finding the perimeter of a rectangle is P=2(l+w) where P is perimeter, l is the length and, w is width
P=20 ft ,l=7ft but w=?
P=2(l+w) 6ft=2w
20ft=2(7ft+w) 6ft/2=2w/2
20ft=14ft+2w 3ft=w
20ft-14ft=14ft-14ft+2w
Therefore the width is 3ft