The weight of a rock on the moon is 200.6N. What is its mass on the earth? (Take g of earth = 9.8 m/s² and g of the moon = 1.7 m/s²)

Given,
Weight of the rock on the moon, ${\mathrm{W}}_{\mathrm{m}}=200.6\mathrm{N}$
Acceleration due to  gravity on the surface of the earth, $g_m=9.8m/s^2$
Acceleration due to  gravity on the surface of the moon, $g_m=1.7m/s^2$

We know, 
Weight, $\mathrm{W}=\mathrm{m}\times \mathrm{g}$
$⟹\mathrm{m}=\frac{\mathrm{W}}{\mathrm{g}}$

$⟹\mathrm{m}=\frac{{\mathrm{W}}_{\mathrm{m}}}{{\mathrm{g}}_{\mathrm{m}}}$
 $\mathrm{m}=\frac{200.6}{1.7}$
 $\mathrm{m}=118\mathrm{kg}$

The mass of an object is constant and does not change from place to place.

Hence, the mass of the rock on the earth = mass of the rock on the moon = 118 kg