According to Newton's third law,every force is accompanied by an equal and opposite force. How then can anything move?

$A$ girl of mass $50\, kg$ jumps out of a moving boat of mass $300\, kg$ on to the bank with a horizontal velocity of $3\, m s^{-1}$. With what velocity does the boat begin to move backwards (in $, m s^{-1}$)?

According to the third law of motion,action and reaction

Two friends,Girish and Neeraj,were discussing Newton's third law. They were perplexed about how action and reaction are equal and opposite. They could not think of an experiment by which they could ascertain this fact. Pushkar,who was their friend,told them that he would set up an experiment to prove this to them. By performing an experiment,Pushkar demonstrated the law.
$(a)$ Can you think of an experiment by which you can demonstrate this law?
$(b)$ What values do you think Pushkar has?

Look at the diagram below and answer the following questions:
$(i)$ When a force is applied through the free end of the spring balance $A$,the reading on the spring balance $A$ is $20 \ g \ wt$. What will be the reading shown by the spring balance $B$?
$(ii)$ Write the reason for your answer.
$(b)$ If a balloon is filled with air and its mouth is untied,air is released from its mouth in the downward direction. Write the other observations made by you and justify your answer.

$A$ gun recoils after firing to conserve