A flagstaff of 5 mts high stands on a building of 25 mts high. For an observer at a height of 30 mts, the flagstaff and the building subtend equal angles. Then the distance of the observer (in mts) from the top of the flag staff is

A

$$3\sqrt{6}$$

B

$$\frac{3}{2}\sqrt{6}$$

C

$$\frac{5}{2}\sqrt{6}$$

D

$$5\sqrt{6}$$