a professor drives 325 miles in 5 hours in order to attend a conference. it appears that he uses 20 gallons of gasoline which costs him a total of $51.2. he conducts a 2 hour training session in the conference , for which he earns a honorary token money of $200 compute the gasoline cost rate as dollars/gallons unit. $2.56 $2.56/gallon $4/gallon