A quantity of 0.020 mole of a gas initially at 0.050 L and 20C undergoes a constant-temperature

Question:

A quantity of 0.020 mole of a gas initially at 0.050 L and 20°C undergoes a constant-temperature expansion until its volume is 0.50 L. Calculate the work done (in joules) by the gas if it expands
(a) Against a vacuum
(b) Against a constant pressure of 0.20 atm.
(c) If the gas in (b) is allowed to expand unchecked until its pressure is equal to the external pressure, what would its final volume be before it stopped expanding, and what would be the work done?