Since most thermodynamic properties are a function of two or more variables $($e$.$g$.$ the volume of an ideal gas is a function of $P,N,$ and $T),$ you will need to review your multi$-$variable calculus. Calculate in terms of $P,T,V_{?},$ and any relevant constants for

a$)P{V}_{?}=RT,$ where $R$ is a constant $($the ideal gas law$),$

b$)P=\frac{RT}{V_{-}b}-\frac{a}{V_{V_{+}b}},$ where $a,b$ and $R_{-}$are constants.