Problem
Suppose that Omar's marginal utility for each additional cup of coffee is 3.5 utils per cup no matter how many cups he drinks. On the other hand, his marginal utility per doughnut is 11 for the first doughnut he eats, 10 for the second he eats, 9 for the third he eats, and so on (that is, declining by 1 util per additional doughnut). In addition, suppose that coffee costs $1 per cup, doughnuts cost $1 each, and Omar has a budget that he can spend only on doughnuts, coffee, or both. What is the minimum value of Omar's budget if he purchases one cup of coffee?