Answer
$15.8\ ft/s$, $71.6^\circ$
Work Step by Step
1. Draw a diagram as shown.
2. The resulting speed of the balloon (blue arrow) will be $v=\sqrt {15^2+5^2}=5\sqrt {10}\approx15.8\ ft/s$
3. The angle with the horizontal is $\theta$ and $tan\theta=\frac{15}{5}=3$, thus $\theta=atan(3)\approx71.6^\circ$
