Boyle Law help...

[hecate]

can anyone tell me the steps to do this problem?

You are given a gas that you measure under a pressure of 720 mmHg. When the pressure is changed to 760 mmHg, the volume becomes 580 mL. What was the original volume of the gas?

I don't know how to do this problem. thanx!

[Warr]

Its this simple ratio:

\frac{P_{1}}{V_{1}} = \frac{P_{2}}{V_{2}}

so to find V_{1}

V_{1} = \frac {P_{1}V_{2}}{P_{2}}