1. A pipe fills a pool in 4 hours, another pipe drains a full pool in 6 hours. How long will it take to fill the pool if both pipes are opened?

2. A pool is connected with 3 pipes. Two pipes fill the pool and one drains it. It takes 3 hours for first pipe to fill the pool and 2 hours for the 2nd one. The third pipe drains a full pool in 6 hours. How long will it take to fill the pool if all pipes are opened?

Ugh, they seem so simple lol, but I can't solve them, just a few guidelines would help..

I'm off to sleep now, so thanks to anyone who helps.