This problem has me stumped!

A stone dropped into a pond creates a circular ripple whose radius expands at the rate of 1.5 ft/sec. Assuming the initial radius of the circle is 0, find the number of square feet enclosed by the ripple after one minute.

Now, I know I have to use (pi)r^2. I'm just not sure where the 1.5 feet and 60 seconds would fit in.