[Sh4d0wD3v1L]

Trig like this is easy. The solution to most problems is draw a picture with a right triangle in it, and solve the missing side.

So, the building will be the leg (going bottom to top) and the shadow will be the base.


|(angle?)
|(building) 180ft (adjacent to angle)
|
|
|__________________
(shadow) 70ft (opposite of angle)

Now, you use the SOH-CAH-TOA to find which one to use...
(Sin=opposite/hypotenuse Cos=adjacent/hypotenuse Tan=opposite/adjacent)
In this case, the angle you are looking at, and the numbers you are given, you have the OPPOSITE (70ft shadow) and the ADJACENT (180ft bldg) sides to the angle.

Now, get out your calculator.
Make sure, first of all, your calculator is in DEGREE mode (hit the MODE key and look for it)
Hit the 2nd key, then tan. This the inverse tangent. This will give you the angle measure given 2 sides. Put 70/180 and close parentheses.

tan-1(70/180) = angle
tan-1(70/180) = ~21.25 degrees

Hope this helped, and feel free to ask if you need anything else.