for #1you want dV/dt = 4pi r^2 dr/dtdr/dt=dV/dt/(4piR^2).

you know dr/dt and r don't you ?

For #2

x^2 + y^2 = 16.

differentiate 2xdx/dt + 2ydy/dt = 0

you know dy/dt, x , and y don't you?

once you have #1 and # 2 then the others should be no problem