In this case, we'll have to carry out several steps to find the solution.
Step 01:
Data
Triangle 1:
b = 15
h = 39
Triangle 2:
h = 36
x = ?
Step 02:
We must apply the rules of similar triangles to find the solution. .

39 * x = 15 * 36
x = (15 * 36 ) / 39
x = 13.8
The answer is:
x = 13.8