The volume of the gas is
This appears to be a Boyle's Law problem.
Boyle's Law is
#color(blue)(bar(ul(|color(white)(a/a)P_1V_1 = P_2V_2color(white)(a/a)|)))" "#
We can rearrange Boyle's Law to get
#P_1 = P_2 × V_2/V_1#
In this problem,