A heating system transfers 180 kJ usefully. Its efficiency increases from 60% to 75% after insulation is fitted.
How much less input energy is needed to transfer the same useful energy?
27 kJ27\ \mathrm{kJ}27 kJ
45 kJ45\ \mathrm{kJ}45 kJ
60 kJ60\ \mathrm{kJ}60 kJ
120 kJ120\ \mathrm{kJ}120 kJ