设正方形的边长为a厘米,
则(a-8)×3=a+16,
3a-24=a+16,
2a=40,
a=20;
(20-8+20+16)×20÷2,
=48×20÷2,
=960÷2,
=480(平方厘米);
答:梯形的面积是480平方厘米.