Bill does 1500 j of work on a lever, which is a simple machine. the lever does 1350 j of work on a stone.

what is the efficiency of the lever?

0.9%
1.1%
90%
111%

Efficiency is the measure of how much work or energy is conserved in a process. In many processes, work or energy is lost, for example as waste heat or vibration. The efficiency is the energy output, divided by the energy input, and expressed as a percentage.
Efficiency is the energy output, divided by the energy input, and expressed as a percentage. 
Efficiency = (1350/1500)×100
                = 90%