The sum of two opposite sides of the described quadrangle is 27 cm, find its perimeter.

1. The sums of the opposite sides of the described quadrilateral are equal, therefore, if for two opposite sides a and c the equality is true:

a + c = 27,

then for the other two opposite sides we can also assert:

b + d = 27.

2. The perimeter of such a quadrangle, of course, is equal to twice the value of this sum:

P = a + b + c + d = 2 (a + c) = 2 * 27 = 54 (cm).

Answer. The perimeter of the quadrangle is 54 cm.