Hey guys, I need some help with some integration problems. Some I could solve already but there are two where I need help. If you can help me, however, please don't just say me: integrate this, but also show me how to do it, that would be really nice. Thanks a lot for everyone who helps me.

1: A large bottle with, 4m high and with a radius of 2m, loses water. Originally, the bottle was full and lost water at a rate proportional to the square root of the depth of the remaining water.

I'm given that the depth of the water is 1m after 2 hours. The question is after how many hours the tank is empty. Please help me with this question.

2. In a freezing machine the temperature is constantly 5 degree. An 100 degree hot object is put in it. One minute later the object is only 80 degree hot. When will it reach a temperature of 10 degree?

Thanks a lot for every advice. But please also give me explanations if you can. I very much appreciate any help. Thanks a lot.