The rate of flow $Q = a \times v$, where $v = \sqrt{2gh}$. Given $a = 2 \text{ mm}^2 = 2 \times 10^{-6} \text{ m}^2$, $h = 2 \text{ m}$, $g = 10 \text{ m/s}^2$. $Q = 2 \times 10^{-6} \times \sqrt{2 \times 10 \times 2} = 2 \times 10^{-6} \times \sqrt{40} \approx 2 \times 10^{-6} \times 6.32 = 12.64 \times 10^{-6} \text{ m}^3/s$.