In this compound, we have two elements Cd (Cadmium) and S (Sulfur), and in order to determine the oxidation number or state, we need to at least know the oxidation number of the other element, since we need to counterbalance and match both values.
Even though Sulfur has some possibilities as oxidation number, the most usual is the same as Oxygen, -2 as charge, therefore Cadmium must have an oxidation number of +2, in order to match both values
Answer = +2, number 5