Aguy walks into the store and steals $100 bill from the register without the owner’s knowledge. he comes back 5 minutes later and buys $70 worth of goods with the $100 bill. the owner gives him back $30 in change. how much money did the owner lose?

The answer is $100
first the guy steals $100 from the owner. Therefore that $100 is a direct loss for the owner. 
the same guy comes and pays $100 for goods worth $70. and the balance is paid back to the guy. 
So the owner gets 100 and pays back 30 and gives goods worth 70. Therefore that transaction is cancelled as the amounts have been paid and no net effect with that transaction . the owner gets 70 for the goods he sold so that transaction wont lose his money. the fact that the guy paid for the bill with the money he stole isn't relevant here as the transaction has been completed
so the only loss for the owner is the $100 the guy stole at first 
answer is $100

Iwish i knew the answer but i don’t but someone will come and us

The answer is why would a teacher ask that