The top of a water tank is open to air and its water level is...

Volume of water flowing out$= Av$, where $A$ is area of opening and $v$ is speed of water from the opening.

$\text{Volume} = \pi{r}^{2}v$

$0 . 74\left(\dfrac{{m}^{3}}\min\right) = \left(3.14 \times {\left(2 \times {10}^{- 2}\right)}^{2} \times \sqrt{2 \times 10 \times H}\right)\dfrac{{m}^{3}}{s} \times \dfrac{60s}\min$

$⇒ H = {\left(\dfrac{0.74}{60 \times 3.14 \times 4 \times {10}^{- 4}}\right)}^{2} \times \dfrac{1}{20}$

$⇒ H = 4.8m$

Hence, the height of water in the tank was $4 . 8m$ from the bottom of the tank.