<u>Answer:</u>
At time 2t the paint ball is at 8 cm to the right and 16 cm to the bottom
<u>Explanation:</u>
We have equation of motion ,
, s is the displacement, u is the initial velocity, a is the acceleration and t is the time.
Considering the horizontal motion of paint ball
Distance traveled during time t = 4 cm
Initial velocity = u m/s
Acceleration = 0 
So 
Now at time 2t,

So horizontal distance traveled in time 2t = 8 cm to the right
Now considering the vertical motion of paint ball
Distance traveled during time t = 4 cm
Initial velocity = 0 m/s
Acceleration = -g 

At time 2t,

So vertical distance traveled in time 2t = 16 cm to the bottom
It is balanced force nothing is being applied I did this already
I would say your answer is B, since Newton's 3rd law is, "For every action, there is an equal and opposite reaction."
It's talking about pairs of actions. Sorry if I'm wrong.