The efficiency of any machine is given by:
efficiency = output obtained / input given
Substituting the values,
Efficiency = 105 / 150
Efficiency = 0.7
Converting this to a percentage, the efficiency of the hammer is 70%.
This is a fairly high efficiency, and this is due to the fact that the hammer is a simpler machine. The more complex a machine is, the greater are the losses in it due to friction, meaning there is a lower efficiency.