Pipe A can fill the tank in 45 min and pipe B can empty the tank in 1 hour 30 min. If pipe B is opened after 30 min of start of pipe A, what is the total time required to fill the tank?
1
1 hour
2
1 hour 10 min
3
1 hour 20 min
4
1 hour 30 min
5
1 hour 15 min