Answer
$M_A-M_B=1.76\times10^{24}kg$
Work Step by Step
The mass of the robot $m=5450kg=5.45\times10^3kg$. Both planets have radius $r=1.33\times10^7m$. Gravitational constant $G=6.67\times10^{-11}Nm^2/kg^2$
On planet A, the weight of the robot is
$$W_A=G\frac{mM_A}{r^2}=2.06\times10^{-21}M_A$$
On planet B, the weight of the robot is
$$W_B=G\frac{mM_B}{r^2}=2.06\times10^{-21}M_B$$
We have $W_A-W_B=3620N=3.62\times10^3N$. Therefore, $$(M_A-M_B)\times2.06\times10^{-21}=3.62\times10^3$$ $$M_A-M_B=1.76\times10^{24}kg$$
