Answer
$t = 28.9~s$
Work Step by Step
We can find the components of the boat's velocity relative to the ground:
$v_x = (8.0~m/s)~sin~30^{\circ}-2.0~m/s = 2.0~m/s~(west)$
$v_y = (8.0~m/s)~cos~30^{\circ} = 6.93~m/s~(north)$
The time to cross the river depends on the north component of the boat's velocity relative to the ground.
We can find the time it takes to cross the river:
$t = \frac{200~m}{6.93~m/s}$
$t = 28.9~s$
