Lol...
Am I reading correctly that you would like us to do your homework for you?
I can give you a hint.
On the first one- Minimizing the surface area of a container for a given volume means getting it as close to spherical as possible.
The second- The key to solving it is that the diagonal of the square garden will be the diameter of the circle. Find the dimensions of the garden. It's simple trig from there out.