Draw a right triangle to model the problem.
The height of the building (opposite side) is the vertical height of the triangle.
The horizontal (adjacent side) at the lower end of the height is the ground.
The hypotenuse, of length = x, is the ramp.
The given angle between the horizontal (adjacent side) and the hypotenuse is 15°.
By definition,
cos(15°) = adjacent/hypotenuse = 10/x
x*cos(15°) = 10
x = 10/cos(15°) = 10.353
Answer: The length of the ramp is 10.4 ft (nearest tenth)