Answer:
11 ft
Step-by-step explanation:
Angle of repose is the angle at the base of the cone. See attached.
A right angle is 90°.
Unless otherwise specified, a cone is a right cone, with apex directly above center of circular base.
The triangle with vertices at apex of cone, center of base, and some point on the boundary circle of base is a right triangle.
All right triangles have two acute angles adding to 90°. If one of them is 45°, so is the other. It follows that the two legs, opposite equal angles, are equal.
The radius of the cone and the height of the cone are two legs on a right triangle with both acute angles 45°, and the radius is 11ft, so the height is also 11ft.
