Correct Answer - Option 2 : 14π
Concept:
Rate of change of 'x' with respect to 't' is given by \(\rm \frac {dx}{dt}\)
Calculation:
Given r = 7cms
Area of a circle A = π r2
\(\rm {dA \over dr}\) = 2πr
At r = 7cms
\(\rm {dA \over dr}\) = 2π × 7
\(\rm {dA \over dr}\) = 14π
