IF I'M NOT RIGHT CORRECT ME!!!
Answer:
The length of the support piece is 25 inches
Explanation:

First, set up the proportion for similar triangles:
30*h=(2.5)*(20)
30h=50
Step 2: Divide both sides by 30.
30h/30=50/30
h=5/3
5/3ft * 15 inches = 25 inches
Turn feet into inches that is: Length of the support piece is 25 inches