Answer
$6.4s$
Work Step by Step
First of all, we find the velocity of the boat relative to water as
$\vec{v_{bw}}=6.1\frac{m}{s}cso25^{\circ}\hat x+6.1\frac{m}{s}sin25^{\circ}\hat y$
$\vec{v_{bw}}=(5.5\frac{m}{s})\hat x+(2.y6)\hat y$
We find the velocity of the boat relative to the ground as:
$\vec{v_{bg}}=(5.5\frac{m}{s})\hat x+(2.6\frac{m}{s}-1.4\frac{m}{s})\hat y$
$\vec{v_{bg}}=(5.5\frac{m}{s})\hat x+(1.2\frac{m}{s})\hat y$
Now we can find the required time:
$t=\frac{\Delta x}{v_{bg,x}}$
We plug in the known values to obtain:
$t=\frac{35}{5.5}$
$t=6.4s$
