The force of attraction between two bodies of mass M1 and M2 separated by a distance r is given by the Newton's law of universal gravitation as G*M1*M2/r^2
Here the mass of the object is 50 kg. The mass of the Moon is 7.36*10^22 kg. The radius of the Moon which is the distance that separates them is 1.738 x 10^6 m.
The weight of the object on the Moon is the force of gravitational attraction between the object and the Moon. That gives W = G*50*7.36*10^22/(1.738 x 10^6)^2, where G is 6.674*10^-11 M/m^2*kg^2
W = 6.674*10^-11*50*7.36*10^22/(1.738 x 10^6)^2 N
=> 81.308 N
The weight of the object on the Moon is 81.308 N