From a tower 18 m high the angle of elevation of the top of a tall building is 45° and the angle of depression of the bottom of the same building is 60°. What is the height of the building in metres?

A

$$12 + 6 \sqrt{3}$$

B

$$6(3 + \sqrt{3})$$

C

$$18 + \sqrt{2}$$

D

$$6(3 + \frac{\sqrt{3}}{2})$$