A boat is rowed across a river at the rate of $4.5km/hr$. The river flows at the rate of $6km/hr$. The velocity of boat in $m/s$ is:

The correct option is A $2.1$
Given,
$v_{Br}=4.5km/hr$
$V_{\text{river, ground}}=6km/hr$
Then,
$V_{\text{boat, ground}}=(6\hat{i}+4.5\hat{j})km/hr=(6\hat{i}+4.5\hat{j})\times \frac{5}{18}m/s$
$V_{\text{boat, ground}}=\sqrt{6^2+{4.5}^2}\times \frac{5}{18}$
$=1.5\times 5\times \frac{5}{18}$
$=\frac{37.5}{18}=2.1m/s$