# A tank can be filled with water by two pipes P and Q together in 36 minutes

A tank can be filled with water by two pipes P and Q together in 36 minutes. If the pipe Q is stopped after 30 minutes, the tank is filled in 40 minutes. The pipe Q can alone fill the tank in time

(a) 60 minutes

(b) 70 minutes

(c) 90 minutes

(d) 100 minutes