i m stuck on both of these please help..

a.

If a force of 90 N stretches a spring 1 m beyond its natural length. how much work does it take to stretch the spring 5 m beyond its natural length?

b.

to design the interior surface of a huge staiinless-steel tank, you revolve the curve y = x^2, 0 <= x <= 4, about the y axis. the container with dimensions in meters, is to be filled with seawater, which weighs 10,000N/m^3. how much work will it take to empty the tank by pumping the water to the tanks top??