water is being pumped to empty a swimming pool.

At 6 a.m , the water level is 150 cm . Every 2 hours , the water level drops by 30 cm. 
what is the earliest time when the pool will be empt ??

A)10 A.M.
B)11 A.M.
C) 4 P.M. 
D) 5 P.M.