The formula for the perimeter of a rectangle is P = 2L + 2W
you are given P (perimeter) and l (length.
Replace the letters withe the given information and solve for width:
76 = 2(31) +2W
Simplify:
76 = 62 + 2w
Subtract 62 from both sides:
14 = 2w
Divide both sides by 2:
W = 14/2
W = 7 cm
The width is 7 cm.