A tower stands on the top of a building which is 40 metres high. The angle of depression of a point situated on the ground from the top and bottom of the tower are found to be 60° and 45° respectively. What is the height (in metres) of tower?

A

$$20\surd3$$

B

$$30(\surd3 + 1)$$

C

$$40(\surd3 - 1)$$

D

$$50(\surd3 - 1)$$