I remember two years ago when I learned what the angle of elevation is xD!
The following picture is drawn with sketchometry:
The angle of elevation is essentially how much two lines intersecting are elevated when moved north/up. Overlap your two hands. Now bring one up. The angle they form is the angle of elevation!
Assume ABCD is the 2D building, and point E is the point from the ground in the question. Using SOH-CAH-TOA (Sine=opposite/hypotensuse-Cosine=adjacent/hypotenuse-Tangent=Opposite/adjacent) we get with some trig rules: 20.7