An object of mass of 78 kilograms is lifted through a height of 6 meters. how much work is done?

The potential energy of an object is

                         (mass) x (gravity) x (height above something).

When the object rises to a greater height, its potential energy is greater.
If it didn't have rocket engines on it, then that extra energy had to from
outside, like from work done by whatever lifted it.

When the 78-kg object is lifted through 6 meters, its potential energy ...
above the place where it started ... is

                           (mass) x (gravity) x (height) =

                            (78kg) x (9.8m/s²) x (6 m) =

                                     4,586.4 kg-m²/sec²  =  4,586 joules

That's the amount of work required to lift it to the new height.