1) The volume of a sphere is . We know that the volume and radius are functions of time here, hence, using implicit differentiation:

Hence:

You know what is, and you know what the radius is at our point of interest. So plug them in!

2)

You could take out a factor of y on the LHS, and then move all other terms to the RHS, giving you a nice explicit function to differentiate. Or you could go about it using implicit differentiation!

Then use the quotient rule!

Or

Rearrange and remember to substitute in y again from the fact that .