Calculus

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The volume of a cone of radius r and height h is given by V=(1/3)pir^2h. If the radius and the height both increase at a constant rate of 2cm/s at which rate in cubic cm/s is the volume increasing when the height is 8cm and the radius is 6cm.
So The answer is 108 pi.
Here's what I did. I thought that dr/dt=2 and dh/dt=2 looking for dv/dt when h=8 and r=6
so dv/dt=(pi/3)*36*2 + (2pi/3)*6*8*2
I got 88pi....that is wrong....what did I do wrong :'(

Thanks

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