$***$ piece of sandstone with a bulk volume of $1\mathrm{.}3$ cc is contained in a $5-$cc cell filled with helium at $760$ mm Hg$.$ Temperature is

maintained constant and the cell is opened to another evacuated cell the same volume. The final pressure in the two vessels is $334\mathrm{.}7$ mm Hg$.$ What is the porosity of the sandstone? given P$1$V$1=$P$2$V$2$

where P$1$V$1=760(5-1\mathrm{.}3(1-$porosity$)$ and P$2$V$2=334\mathrm{.}7(10+?).$

please solve for the porosity using the steps provided above and also finish what is V$2?$ equal to and why.