The ground, the building, and the ladder form a right triangle, in which
the leaning ladder is the hypotenuse.
For the angle between the ladder and the ground, the 4-ft along the ground
is the side adjacent to the angle, and the 7-ft ladder is the hypotenuse.
(adjacent side) / (hypotenuse) = cosine of the angle.
Cosine(a) = 4/7 = 0.57143... (rounded)
Angle 'a' = 55.15 degrees (rounded)
