The acceleration of gravity on the Moon is [tex]g=1.62 m/s^2[/tex]. The weight W is related to the mass of the object m by the relationship
[tex]W=mg[/tex]
If we rearrange it and we use [tex]W=0.50 N[/tex], we find the mass of the object on the Moon:
[tex]m= \frac{W}{g}= \frac{0.5 N}{1.62 m/s^2}=0.3 kg [/tex]
But the mass is an intrinsic property of an object, therefore it does not change if we are on the Moon or on Earth: therefore, 0.3 kg is also the mass of the object on Earth.