See picture below for a geometric view.
Let x = height of building
We use basic trigonometry to find x.
The tangent function = opposite side of right triangle OVER adjacent side of right triangle.
tan(2°) = x/1
Solve for x.
After multiplying both sides by 1 (here 1 represents 1 mile), we get
tan(2°) = x.
We now use the calculator to find x.
In fact, you can take it from here. Use your calculator.