Your grandfather gives you the keys to his car and money to fill it up. He insists on you using 91-octane gasoline (gasoline with an octane rating of 91). When you get to the pump, the station is out of 91 -octane gasoline, but they have 87 - and 93 -octane. The prices for the three products are $3.30/ gallon for 87 -octane, $3.80 /gallon for 91 -octane, and $4.05/ gallon for 93 -octane. You decide to blend the 87 - and 93 -octane to approximate the 91 -octane that your grandfather wants. Take the system to be the car's tank and the process to be filling the tank. Is the system open or closed? Is the process steady or unsteady? Assume that the volumes of the gasolines are additive and that the octane rating of the blended product depends linearly upon the volume fractions of the components. What is your cost per gallon for the self-blended 91 -octane? $ /gallon