c
$\mathrm{C}_{\mathrm{V} \operatorname{mix}}=\frac{\mathrm{n}_{1} \mathrm{CV}_{1}+\mathrm{n}_{2} \mathrm{CV}_{2}}{\mathrm{n}_{1}+\mathrm{n}_{2}}$
$\frac{\mathrm{n}_{1}}{\mathrm{n}_{2}}=\frac{1}{2} \mathrm{CV}_{1}=\frac{\mathrm{f}_{1}}{2} \mathrm{R} \mathrm{CV}_{2}=\frac{\mathrm{f}_{2}}{2} \mathrm{R}$
$\frac{13}{6} \mathrm{R}=\frac{\frac{\mathrm{n}_{1} \mathrm{f}_{1}}{2} \mathrm{R}+\frac{\mathrm{n}_{2} \mathrm{f}_{2} \mathrm{R}}{2}}{\mathrm{n}_{1}+\mathrm{n}_{2}}$
$\frac{13}{3}=\frac{\frac{\mathrm{n}_{1}}{\mathrm{n}_{2}} \cdot \mathrm{f}_{1}+\mathrm{f}_{2}}{\frac{\mathrm{n}_{1}}{\mathrm{n}_{2}}+1}$
$\mathrm{f}_{1}+2 \mathrm{f}_{2}=13$
$f_{1}=3 \quad f_{2}=5$