Hess's Law/Enthalpy of reaction
If you add up the enthalpies of the following reactions with the given factor and divide the result by two you will get the desired result.

$$\ce{CH4 + 2 O2 -&gt; 2 H2O + CO2} \tag{· 2}$$
$$\ce{2 C + H2 + 3 Cl2 -&gt; 2 CHCl3} \tag{· 1}$$
$$\ce{C + O2 -&gt; CO2} \tag{· -2}$$
$$\ce{2H2 + O2 -&gt; 2 H2O} \tag{· -2}$$
$$\ce{2 HCl -&gt; H2 + Cl2} \tag{· -3}$$

$$\ce{2 CH4 + 6 Cl2 -&gt; 6 HCl + 2 CHCl3}$$