Answer:
75 m
Explanation:
The horizontal motion of the projectile is a uniform motion with constant speed, since there are no forces acting along the horizontal direction (if we neglect air resistance), so the horizontal acceleration is zero.
The horizontal component of the velocity of the projectile is

and it is constant during the motion;
the total time of flight is
t = 5 s
Therefore, we can apply the formula of the uniform motion to find the horizontal displacement of the projectile:

The functions of angles are used to find unknown lengths or angles that can't be measured, in terms of known quantities. The trig functions of angles are ratios of lengths, so they're bare naked numbers without units.
Newton's third law states that for every action, there is an equal and opposite reaction. When you let go of the ballon, you are letting the force out but the force also pushes the balloon back.
It would connect the Earth of the device to Live, causing the metal casing of the device to become Live, touching it would cause a serious electrical shock.