A man walking away from the foot of a cliff 150 meters high observes that it take 2 minutes to change the angle of elevation of the top of the cliff from $$60^{\circ}$$ to $$45^{\circ}$$. His walking speed in kmph is

A

$$\frac{9+3\sqrt{3}}{2}$$

B

$$\frac{9-3\sqrt{3}}{2}$$

C

$$\frac{3(1+3\sqrt{3})}{2}$$

D

$$\frac{3(\sqrt{3}-1)}{2}$$