Alan bought 36 gallons of gas for $2.05 per gallon.
total amount of gas = 36 gallons
Price of one gallon = $2.05
So, for the price of 36 gallons : Multiply the amount of 1 gallon with the the number of gallon
Price of 36 gallons = 36 x 2.05
Price of 36 gallons = $73.8
Alan spend an amount of $73.8 on the gas of 36 gallons
Answer : $73.8