Final answer:
Ella's utility function, if she likes her coffee with 3 teaspoons of sugar per cup, should directly link her coffee consumption with her sugar preference. The appropriate utility function is U(x1, x2) = 3x1 + x2, showing that each cup of coffee contributes thrice as much to her utility as each teaspoon of sugar.
Step-by-step explanation:
When writing Ella's utility function, which indicates the satisfaction she derives from drinking coffee with sugar, we take into account that she prefers 3 teaspoons of sugar per cup of coffee. Therefore, we must express her utility in terms of both cups of coffee (x1) and teaspoons of sugar (x2).
To accurately represent her preferences, we recognize that every cup of coffee Ella drinks is linked with precisely three teaspoons of sugar for maximum utility. Thus, if Ella consumes one cup of coffee, her utility increases not just by the coffee alone but also by the sugar in it. Since each cup of coffee (x1) requires three teaspoons of sugar to provide utility, her utility function would involve the coffee multiplied by three, plus the sugar consumed separately. Hence, the correct representation of Ella’s utility function would be U(x1, x2) = 3x1 + x2, indicating that each cup of coffee has threefold the impact on her utility in relation to each teaspoon of sugar.