Assuming the building meets the ground at right angles, the right triangle formed has side length 10 ft and hypotenuse 15 ft. Then the other side length (d) is given by the Pythagorean theorem as ...
d² + 10² = 15²
d² = 225 -100 = 125
d = √125 = 5√5 ≈ 11.2 . . . feet
The bottom of the ladder is about 11.2 feet from the building
