$\begin{aligned} \frac{d \varepsilon}{d t} &=7 \mathrm{~cm} / \mathrm{sec} . \\ A &=\pi \varepsilon^{2} \\ \frac{d A}{d t} &=2 \pi \varepsilon \frac{d \varepsilon}{d t}-(1) \\ \text { Radius after } 10 \text { minutes } ; & \varepsilon=70 \mathrm{~cm} \times 60 \mathrm{~cm} \\ \frac{d A}{d t} &=2 \times \frac{22}{7} \times 70 \times 7 \times 60[\mathrm{Put} \text { in (1)... }\\ &=1,84,800 \mathrm{~cm}^{2} / \mathrm{sec} . \end{aligned}$