My friend and I are planning to make music in his garage. There's no electricity so we're going to buy a generator. We're not sure how long the electricity will last, though. Lets say the generator is 600 watts and the music machine(MPC 2000XL) is 24 watts, the speakers are 40, and the lights are around 100 watts, how long will the power last?

I'm regretting not taking physics at this point.

Please help.