Answer:
x = 4
Explanation:
Since the rectangles are similar, use a ratio.
15/6 = 10/x
or
6/15 = x/10
I will use 15/6 = 10/x to solve this problem, but both ratios should work to solve this problem.
15/6 = 10/x
Cross Multiply:
6(10) = 15x
Solve:
60 = 15x
x = 4