Answer : $\;\large\frac{19}{13}$
Explanation :
$C_{peq} = \large\frac{n_{1}C_{p_{1} }+ n_{2} C_{p_{2}}}{n_{1}+n_{2}}$
$C_{veq} = \large\frac{n_{1} C_{v_{1}}+n_{2} C_{v_{2}}}{n_{1}+n_{2}}$
$r_{eq} = \large\frac{C_{peq}}{C_{veq}} = \large\frac{\large\frac{2 \times \large\frac{7}{2}+1\times \large\frac{5}{2}}{3}}{2 \times \large\frac{5}{2} + 1 \times \large\frac{3}{2}}$
$=\large\frac{19}{13}$