As a circular griddle is being heated, its diameter changes at a rate of 0.01 cm/min. When the diameter is 30 cm, at what rate is the area of the griddle changing?

I know my formula is V=PI*r^2

and i know since i am given a diameter i would use (h/2) for my radius.

but once i take my derivative of the area formula and plug in my diameter and my DD/DR as .01 cm/min, i am given .942...

the answer is .471

what am i doing wrong?