Do you include revenue and expenses ONLY?

What is the net income given this financial statement:
Accounts receivable $5,000
Sales revenue $75,000
Cash $15,000
Salaries expense $20,000
Rent expense $10,000

Basically, what I did, was, I thought you were supposed to just subtract the total of all expenses from the revenue, which as a result I got $45,000... but then I added cash and accounts receivable and ended up with $65,000 which was wrong, lol. Am I not supposed to include or disregard cash and/or accounts receivable when calculating net income?