related rates sphere volume and area calculus problem I  have been given the following problem: 
A spherical balloon is expanding at the rate of 60 pie in^3/sec. How fast is the surface area of the balloon expanding when the radius of the balloon is 4 inches? 
I don't understand how the way I set the problem up is not giving me the correct answer. I have created an equation that links volume to area, did implicit diff. and now I should have only 2 variables, one of which I have the value for, dV/dt.  please see image for how I set up the problem 

You want to know $dA/dt$, so rearrange the equation you have for this quantity, substitute in your expression for $A$ as a function of $r$, and finally evaluate at the value of $r$ given. 
