$v_{sound} = \large \sqrt \frac{\gamma k_BT}{M}$, where $k_B$ is the Boltzman's constant and M is the molar mass of the gas, $\gamma$ is the adiabatic index and T is the temperature.

$v_{sound} H_2 = \large \sqrt \frac{\gamma k_BT}{M} = \large \sqrt \frac{7 k_BT}{5 \times 2.01}$

$v_{sound} CO_2 = \large \sqrt \frac{\gamma k_BT}{M} = \large \sqrt \frac{1.28 k_BT_0}{44}$

$v_{sound} H_2 = v_{sound} CO_2 \rightarrow \large \sqrt \frac{7 k_BT}{5 \times 2.01}$$= \large \sqrt \frac{1.28 k_BT_0}{44}$

$\Rightarrow T_0 = \large\frac{7 \times 44 \times T}{5 \times 2.01 \times 1.28}$

$\Rightarrow T_0 = \large\frac{308 \times T}{12.864} $$ \approx 24 T$