A stone is dropped into a well and progressive waves are moving in circles at a speed of 6cm per second . At the instantt when the radius of circular wave is 15 cm, how fast is enclosed area changing ?

Explanation

To solve the problem step by step, we will follow these instructions:

### Step 1: Understand the problem
We are given that a stone is dropped into a well, creating circular waves that expand outward at a speed of 6 cm/s. We need to find out how fast the enclosed area of the circular wave is changing when the radius of the wave is 15 cm.

### Step 2: Identify the formula for the area of a circle
The area \( A \) of a circle is given by the formula:
\[
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