Hello from MrBillDoesMath!
Answer:
Choice D, 14 ft.
Discussion:
From the Pythagorean thereon, where "h" is how high on the building the ladder reaches,
6^2 + h^2 = 15^2 => as 6^2 = 36 and 15^2 = 225
36 + h^2 = 225 => subtract 36 from both sides
h^2 = 225 - 36 => as 225 - 36 = 189
h^2 = 189 => take square roots of both sides
h = 13.747 ( approximately)
which rounded to the nearest foot is 14 feet. That is Choice D.
Thank you,
MrB