I need help with knowing the oxidation I keep mistaking the subtraction.

Some chemical reactants are listed in the table below. Complete the table by filling in the oxidation state of the highlighted atom. \begin{tabular}{|c|c|} \hline species & oxidation state of highlighted atom \\ \hline H2(g) & \\ \hline I(aq) \\ \hline CuO(s) & \\ \hline H3O(aq)+ & \\ \hline \end{tabular}