Answer: We will recommend him to use standard mileage method
Explanation: Robert is a caterer who travels a lot. Hence he have two options by which he can compute the transportation deduction he is eligible for. These two methods are named as actual expense method and standard mileage method.
As in the given scenario Robert do not actually knows the expense he has incurred so he has to use standard mileage method in which he has to assume the unit cost.
Thus, assuming standard rate to be 0.50 cents per mile he his eligible for a deduction of ( 0.5 cents * 3,000 miles), that is, $1500.