The perimeter can be found by using the formula: P = 2w + 2h
w = width
h = height
P = perimeter
We are given the perimeter of 108 inches.
We are given the width of 18 inches.
Substitute in the formula.
108 = 2(18) + 2h
108 = 36 + 2h
Solve for h.
108 = 36 + 2h
108 - 36 = 36 - 36 + 2h
72 = 2h
72/2 = 2h/2
36 = h
Therefore, the length of the missing side is 36 inches.
Best of Luck!