Let x be the length and y be the width. Then x + y = 23, (1) ( 23 =) xy = 120. (2) Express x = 23 - y from (1) and substitute into (2). You will get (23-y)*y = 120. Solve this quadratic equation: = , = . Factor the left side: (x - 15)*(x-8) = 0. The roots are 8 and 15. The width, or shorter side is 8 cm. The length, or longer side is 15 cm.