Figure below provides operating data for a compressed air energy storage system using off-peak electricity to power a compressor that fills a cavern with pressurized air. The cavern shown in the figure has a volume of 105 m' and initially holds air at 290 K, 1 bar, which corresponds to ambient air. After filling, the air in the cavern is at 790 K. 21 bar. Assuming ideal gas behavior for the air, determine (a) the initial and final mass of air in the cavern, each in kg, and (b) the work required by the compressor, in GJ. Ignore heat transfer and kinetic and potential energy effects.