How to get net income from a trial balance?
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Revenuess less expenses. That's always net income, regardless of where you're getting it from.

Normaly net income is derived from the profit and loss account and not from the trial balance.
You can get the same from trial balance, but in that case you will have to put a extra effort on that.
However it is the difference between Revenue Accounts and Expenses Accounts in your ledger.

This is just homework. There's nothing fancy about a trial balance, and in first chapters, adjusting entries are not even done. So yes they can get the net income off the trial balance (adjusted if appropriate to the chapter) and it will be exactly the same as what will end up on the income statement.