Show that the density of an ideal gas occupying a volume v

Question

(a) Show that the density of an ideal gas occupying a volume V isgiven by ρ = PM/RT, where M is the molar mass. Show this by calculating the following three quantities in terms of M, P, n, R,and T.

        sample mass m =___________

                             V = ___________

                density ρ = ___________

(b) Determine the density of oxygen gas at atmospheric pressure and 85.0°C.

      __________ kg/m3