A laser pulse is sent from ground level to the bottom of a concrete water tank at normal incidence. The tank is filled with water up to $\text{2 m}$ below the ground level. The reflected pulse from the bottom of the tank travels back and hits the detector. The round-trip time elapsed between sending the laser pulse, the pulse hitting the bottom of the tank, reflecting back and sensed by the detector is $\text{100 ns}$. The depth of the tank from ground level marked as $\text{x}$ in metre is ________.
(Refractive index of water $n_{\text{water}}=1.3$ and velocity of light in air $c_{\text{air}}=3 \times 10^{8}\: m/s$)
- $9$
- $10$
- $11$
- $12$