Newton's third law of motion states that for any action, there is equal and opposite force. For a person standing on a floor, the action force is the weight and thus the floor must exert an opposite and equal reaction force equivalent in magnitude to the weight of the person.
In this regard, statement 3. is correct.
Use the kinematics equation:
d = vt + 1/2at^2.
In this problem,
v = 15 m/s.
a = 3 m/s^2,
t = 10 s,
So:
d = 15(10) + 1/2*(3)*(10^2) = 300 meters
