According to third law of Newton , there is equal and opposite reaction to every action . Here force by the parent on child is action and the force by child on parent is reaction . The former is given as 25 N so force by child on parent will also be 25 N .
Magnitudes are measured by intensity so a 3.4 earthquake is much less stronger than a 4.5 earthquake it’s very literally when measuring them the higher the number the stronger it is
