A solar charging unit contains a solar panel connected to a rechargeable battery. The solar panel is 30% efficient. The battery stores 80% of the energy supplied to it.
During a test, the energy in the battery's store increases by 720 J.
How much energy was supplied to the solar panel during the test?
3000 J3000\ \mathrm{J}3000 J
216 J216\ \mathrm{J}216 J
900 J900\ \mathrm{J}900 J
1920 J1920\ \mathrm{J}1920 J