The easiest way to solve this problem would be to use the pythagorean theorem. Plug in the information you know. 25 will have to be c because it is the hypotenuse. You can plug 7 in for a or b. It does not matter which one you plug 7 in for because you will still get the same answer.
This is what it should look like:
7^2 + b^2 = 25^2
Now solve the equation.
7^2 = 49
25^2 = 625
The new equation will be 49 + b^2 = 625
Now subtract 49 from 625.
625 - 49 = 576
b^2 = 576
Now take the square root of both sides to get b by itself.
b = 24
Your answer should be: The ladder reaches 24 ft. high on the building.