4. A one-person automobile oil change in rural Mississippi has a fixed overhead of $900.00 per month. The variable cost per oil change $10.00. The charge is $30.00 for one oil change. If the owner/worker Joe Smith desires to have a contribution per month of $2,100.00, the number of oil changes he should do per month is A) 100 B) 300 C) 150 D) 75 E) none of the above