Oxidation numbers from a formula

You will write three small functions that find an oxidation number by solving the equation of the sums.

The idea. The oxidation numbers of all the atoms add up to the charge of the species. If one element X has n atoms and all the other atoms together contribute others, then $n \times x + \text{others} = \text{charge}$.

Your tasks.

1. In others_total, return the total for n_o oxygen atoms that are each $-2$.
2. In find_ox, return the oxidation number of X from n, others and charge.
3. In oxoanion, return the oxidation number of X in an ion $\text{XO}_m^{q-}$, using the two functions above.