Power and Pumps (lifting objects)

First let's draw a simple diagram and get the information out of the question:

We will be using the formula for gravitational potential energy. This is the SAME as work done, so you could use that too! but as we are lifting a load, it seems appropriate to use the Gravitation potential energy. Now we can plug in our values and calculate the THEORETICAL amount of work done to lift this box. (work is the same as energy)

Work over time will give us power, so now we can calculate the theoretical power required to get this job done:

The value above the is theoretical power. The ACTUAL POWER required comes from a measurement taken from the machine, and this is given in the question. By making a comparison (dividing) between these two values we can calculate how efficient the machine is.