Tony charges $5 to park a car in his parking lot. He pays $40 per day to rent the lot. If 50 cars park in his lot during the day, how much does he earn after expenses?

He earns after expenses: $210

Explanation:

If 50 cars park in his lot during the day, he will earn:

50*$5 = $250

But he must include expenses to know his real profit. The only expense that the problem states is the lot rent, which is $40 per day. Expenses must be subtracted from his earnings:

$250-$40 = $210

On a day, he earns after expenses: $210