Question

a man weight 60 kg on the surface of the earth the altitude where his weight is 15 kg is

Answer 1

On surface of earth, you get g=9.81m/s² acceleration pulling you down. That gave you 60kg reading on the weighing scale. Assuming you won't be moving with respect to the surface of the earth, you would need to go high enough to get 0.5g of the gravitational pull. The gravitational force is calculated as

Force = ( G * M1 * M2 )/d²

where G is the gravitational constant, d is the distance between the two objects weighing M1 & M2.

Now if earth is M1, the acceleration would be (G * M1)/d²