Helium is collected over water at $25C$ and $1\mathrm{.}00$atm total pressure.

a$)$ What total volume of gas must be collected to obtain $0\mathrm{.}586g$ Helium $($vapor pressure of water at $25C$ is $23\mathrm{.}8$ torr$).$

b$)$ Determine the density of helium.