B$)$ A mixture of $H_2(g)$ and $N_2(g)$ has a density of $0\mathrm{.}216\frac{g}{?}$ Litre at $300K$ and at a pressure of $66661\mathrm{.}2$ pa$.$ Consider both $H_2(g)$ and $N_2(g)$ as ideal gases.

Calculate the total number of moles of the mixture of $H_2(g)$ and $N_2(g),$ i$.$e$,$ ntotal $?$