Answer
The mass of Mars is $6.5 \times 10^{23} ~kg$
Work Step by Step
$\frac{GmM}{r^2} = 0.38mg$
$\frac{GM}{r^2} = 0.38g$
$M = \frac{(0.38g)(r^2)}{G}$
$M = \frac{(0.38)(9.80 ~m/s^2)(3.4 \times 10^6 ~m)^2}{6.67 \times 10^{-11} ~N\cdot m^2/kg^2}$
$M = 6.5 \times 10^{23} ~kg$
The mass of Mars is $6.5 \times 10^{23} ~kg$
