Hi Khan! Well I'm not really certain of this solution but give it a try:

1)State the given:

, , so we attempt to find

2)Derive a formula for Volume as a function of diameter:

Volume of a sphere is given as , but since , then

Then we plug r back in to get:

So that by simplifying, we get:

3)Take the derivative of the equation with respect to time:

We get:

Take it from here dude. Remember that you only have to plug in all the values that is on part 1 of this solution. And since it is a negative rate of change