Answer:
If both triangles are similar, the triangles are exactly the same shape, but always not the same size. When you line up these two triangles, you will see that 5ft and 25ft line up and 10ft and x line up. Using a ratio, we can solve for x.
5:25
10:x
Cross multiply.
5x:250
Divide both sides by 5.
x=50
So, x is 50ft.
:)