Min/Max Calculus Problems

Hi, i have two problems of bounded areas which i just don't even know how to start. If you could give me some pointers on how to do bounded area problems in general as well, that would be awesome.

A rectangle is bounded by the x-axis and the semicircle

y= squareroot(25-x^2) what length and wideth should the rectange have so that its are is maximum?

A rectangular package to be sent by a postal service can have a amazimum combined length and girth of 108 inches. Find the dimensions of the package of maximum volume that can be sent.

Thanks a lot.

Aussiekid90