Efficiency is equal to 35 / 125 * 100 which is equal to 28%.
Efficiency is the ratio of the useful work performed by a machine or in a process to the total energy that it consumed.
So basically it is the useful output which in this case was 35 J divided by the total input given to the machine which was 125 J in this case multiplying by 100 to get the percentage.
If we did not need the percentage then we could have simply not multiplied it by 100.
