Devin always drinks his 8 oz of Diet Coke with 2 oz of Captain Morgan. Each beverage drank in this way provides Devin 15 units of utility. Excess Captain Morgan or excess Diet Coke do not add to Devin's utility. Explain the nature of Devin's utility function (e.g., what kind of utility function is this? What is the functional form?), and indicate the form of his indifference curve map (e.g., graph his indifference curves).