Answer:
684.5 is the weight on mars and 1813 on earth
Explanation:
185*3.7=684.5 185*9.8=1813 you multiply for earth by 9.8 because that's the gravity on earth and you multiply by 3.7 because that's the gravity on mars
The initial kinetic energy of the boat and its rider is

After Sam stops it, the final kinetic energy of the boat+rider is

because its final velocity is zero.
For the law of conservation of energy, the work done by Sam is the variation of kinetic energy of the system:

where the negative sign is due to the fact that the force Sam is applying goes against the direction of motion of the boat.
Look at bitesizes physics section, they have all the information you need to complete this question.
The answer is 24N. Since the body is moving with constant velocity all the forces must balance (equal & opposite)