A right triangle is formed with one corner at Dan, another corner, the right angle, at the building (6 feet from the base), and the other corner being the top of the building.
The distance from Dan to the building (6 feet from the bottom) is the adjacent side = 30.
The distance from the building (6 feet from the bottom) to the top of the building is the opposite side = 59.
tan (angle) = opposite / adjacent ---> tan(angle) = 59/30
---> angle = tan-1(59/30)
---> angle = 63°