Answer
(a) The acceleration due to gravity on Mars is $3.75m/s^2$.
(b) A 65-kg person would weigh $243.75N$ on Mars.
Work Step by Step
The gravitational force on an object with mass $m$ by a planet with mass $M$ and radius $r$ has the formula $$F=G\frac{Mm}{r^2}$$
where the acceleration due to gravity can be found by $$a=G\frac{M}{r^2}$$
(a) We have $G=6.67\times10^{-11}Nm^2/kg^2$, $M_{Mars}=6.46\times10^{23}kg$ and $r_{Mars}=3.39\times10^6m$
$$a=G\frac{M_{Mars}}{r_{Mars}^2}=3.75m/s^2$$
(b) Mass of person $m_p=65kg$. The weight of the person is $$W=m_p\times a=65\times3.75=243.75N$$
