The perimeter is given by adding up all the side lengths; we are given all but two of the lengths, which we must calculate:
(1) The unknown side length that joins that which is 18 in. would be equal to 50 - 10 = 40 in.
(2) The unknown side length that joins that which is 10 in. would be equal to 40 - 18 = 22 in.
Thus the perimeter would be equal to:
50 + 40 + 10 + 18 + 40 + 22
= 180 in.