suppose that Doe's dad gave him a tractor-trailer rig from which he generates amonthly total revenue of $25000. His total monthly gas and maintenance costs are $18000. Tractor-trailer rigs identical to that of Doe can be rented for $15000 a month. Doe can also, if he so chooses, work for another firm and earn $5000 a month. Assuming that nothing will change, how will you advise Doe based only on economic profit, given the information provided?