By using a right triangle as a model, we will see that height of the roof is 9.38 ft.
What is the height of the roof of the house?
The slant height is equivalent to the hypotenuse of a right triangle, so we know the length of the base and the hypotenuse of a right triangle. The cathetus will be half of 18ft
We need to find the other cathetus, so we can use the Pythagorean theorem, if X is the other cathetus we will get:
X^2 + (9ft)^2 = (13 ft)^2
X = √( (13 ft)^2 - (9 ft)^2) = 9.38ft
So the height of the roof is 9.38 ft.
If you want to learn more about right triangles, you can read: