What is the power output of an electric motor that lifts a 2.0 kilogram block 15 meters vertically in 6.0 seconds

The block gains gravitational potential energy as it gets higher,
and that's the energy that the motor has to supply.

The amount of potential energy gained by the block is

                    (mass) x (gravity) x (height)

               = (2.0 kg) x (9.8 m/s²) x (15 m)

               =  (2 x 9.8 x 15)  kg-m²/s²  =  294 joules.

Power = (change in energy) / (time for the change)

           =           (294 joules)  /  (6 sec)

           =                 49 joules/second  =  49 watts .