CPM Homework Help : CALC Problem 7-51

An alien uses mysterious powers to make crop circles in a Nebraska wheat field. If the radius of a crop circle increases at the rate of $6$ ft/min, find the rate at which the circle's area is increasing when the radius is $150$ feet.

Step 1:

Start with the geometric equation of the area within a circle. There is no Calculus involved in this step.
$A = πr^²$
Do NOT substitute a value for $r$ , because the $r$ changes. That is where Calculus comes in...

Step 2:

Implicitly differentiate with respect to time, $t$ .