Question

A force of 25N acts on a body at rest for 0.2s and a force of 70 N acts for the next 0.1 s in opposite direction. If the final velocity of the body is 5m/s, the mass of the body is

Answer 1

This your answer. Mass cn be found by the formula of force.
$f = \frac{m(v - u)}{t}$