Answer
$\theta=28.3^{\circ}$ with respect to the ground.
Work Step by Step
Wind's horizontal velocity = $10km/hr=10\times\frac{1000m}{3600s}=2.78m/s$
Vertical velocity $=1.5m/s$
So, with respect to the ground, $\theta=tan^{-1} (\frac{1.5}{2.78})=28.3^{\circ}$
