Answer: 14 feet
=====================================================
Step-by-step explanation:
Check out the diagrams below.
We'll start with the left diagram (marked "before") which is a right triangle with the horizontal leg of 25 feet and hypotenuse 65 feet.
Use the pythagorean theorem to find the vertical side x.
a^2 + b^2 = c^2
25^2 + x^2 = 65^2
625 + x^2 = 4225
x^2 = 4225 - 625
x^2 = 3600
x = sqrt(3600)
x = 60
The top of the ladder is 60 feet high when placed against the wall in this configuration.
------------------
If the upper end is moved down 8 feet, then x-8 = 60-8 = 52 feet is the new height of the ladder. Refer to the "after" in the diagram below.
Like earlier, we'll use the pythagorean theorem to find the missing side.
a^2 + b^2 = c^2
y^2 + 52^2 = 65^2
y^2 + 2704 = 4225
y^2 = 4225 - 2704
y^2 = 1521
y = sqrt(1521)
y = 39
The horizontal distance from the ladder base to the wall is now 39 feet.
Earlier it was 25 feet, so it has increased by 39-25 = 14 feet.