The question presents the reaction for the combustion of methane (CH4), an exothermic reaction, and asks us to choose which change to the system would drive the reaction towards formation of products (to the right).
Since the combustion of methane is a reaction that releases heat - when CH4 and O2 react, they produce CO2, water and heat - decreasing the temperature of the system would deslocate the reaction towards the formation of products (to the right).
The removal of CH4 would have drive the reaction to the left in an attempt to "restore" the reactant removed. Similarly, the addition of CO2 would drive the reaction to the left, in order to "consume" the excess of CO2. Since it is an exothermic reaction, an increase in the temperature would drive the reaction to the endothermic side, which is the reactants side (the left).
Therefore, the best option that describes a change to drive the reaction to the right is (a), "a decrease in temperature".