It would be helpful to draw the figures, you will see that for ABCD there 2 lacking side lengths which are AB and CD. For EFGH, there is one lacking side length which is EH. We use the ratios of the corresponding sides to determine side EH. We do as follows:
FG / BC = EH / AD
10 / 8 = EH / 12
EH = 15
Therefore, the perimeter would be:
15+10+5+15 = 45 units
