Correct Answer - Option 4 : 120π

__Concept:__

The rate of change of the value of a function f(x) with respect to a variable t, is given by: \(\rm \frac {df(x)}{dt}\)

The area of any circle is π r^{2 }where r is the radius of the circle.

**Calculation:**

We know, area of any circle,

A = π r^{2}

Differentiating the equation we get,

⇒ \(\rm dA \over dt\)= 2π r × \(\rm dr \over dt\)

Given, r = 20, \(\rm dr \over dt\)= 20

Putting the values we get,

⇒ \(\rm dA \over dt\) = 2 π × 20 × 3

⇒ \(\rm dA \over dt\) = 120 π

So, the right answer is 120π