A person on walking 20 metres towards a chimney in a horizontal line through its base observes that its angle of elevation of the top of the chimney changes from $$30^\circ$$ to $$45^\circ$$. Then the height(in metres) of the chimney is

A

$$10 \sqrt{3}$$

B

$$10(\sqrt{3} + 1)$$

C

$$20 \sqrt{3}$$

D

20