Answer:
x = 15
Step-by-step explanation:
When figures are similar, the lengths of corresponding sides are in the same ratio.
In the figure, the side measuring 8 corresponds to the side measuring 20. The ratio of the lengths of those two corresponding sides is 8/20.
The side measuring 6 corresponds to the side measuring x. The ratio of the lengths of those two corresponding sides is 6/x.
Since the quadrilaterals are similar, the ratio 8/20 must equal the ratio 6/x.
We use that fact to write an equation, and then we solve for x.
8/20 = 6/x
Reduce the fraction on the left side.
2/5 = 6/x
Cross multiply.
2x = 5 * 6
2x = 30
x = 15
