Math word problems help?

Question

please help me with these word problems.....please show ur work..thankyou so much....i benn trying to do them for hours...

1. An oil tanker can be emptied by the main pump in 4 hours. An auxiliary pump can empty the tank in 9 hours. If the main pump is started at 9am, when should the auxiliary pump be started so that the tanker is emptied by noon?

2.a bathroom tub will fill in 15 minutes with both faucets open ans the stopper in place. With both faucets closed, and the stopper removed, the tub will empty in 20 minutes. How long will it take for the tub to fill if both faucets are open and the stopper is removed?

Answer 1

q1

1/4 + x/9 = 1/(12-9)

x/9 = 1/3 - 1/4 = 1/12

x/9 = 1/12

x = 3/4

auxiliary pump should be working 3/4 of the whole process.

if they stopped at the same time, it should be started at 9:45 am.

q2

2/f = 1/15

1/s = -1/20

2/f + 1/s = 1/15 - 1/20 = 1/60

answer = 60 minutes = 1 hour