Please, go ahead.
You aren't even doing commerce. I hardly see how you can consider yourself to an authority on the matter.
The midwifery thing is just a joke, there is no such combination at unsw. I did fins1612 and got a HD for that subject.
The most obvious reason is that they actually put the company tax rate in the question, a reasonable person would infer that, given the question, the profit would be pre-tax, otherwise why would they give you the tax rate? There is no such thing as absolutely definitive question, otherwise you might as well claim that the question fail to inform you whether earth was invaded by aliens during the particular financial year, hence rendering the payment of tax irrelevant.
The second reason is the one your lecturer told you - based on tutorial questions and class exercises, you should be able to infer that a question of this kind would provide a pre-tax figure. A person who makes this mistake probably either don't do their homework or don't go to class. If a significant number of other students made the same mistake as you, then it's another matter.
Lastly and this is probably what you are trying to argue against - companies are 'taxed' on 'profit'. The thing subject to taxation is 'profit'. Company X makes a profit, and this profit is subject to taxation. Profit making precedes the act of taxing. How then can you assume that profit is post-tax? If this was a 'loss' and not a 'profit', would you also assume the loss is post-tax? That wouldn't make sense because losses are not taxed, right? So unless it explicitly says 'after tax' profit, then it would only be natural to assume the profit is pre-tax.