Currently, you eat a dessert every single day. Doing so brings you a fair amount of enjoyment, but you also know that it will cost your health long-term. You decide to figure out how often you should really be eating dessert.

You feel deprived and unhappy if you don't eat any dessert ever, so the first dessert your eat each week brings you $100 of value. Then the second brings only $60, and then it goes down by $10 each time after that -the third brings $50, the fourth $40, and so on.

Every time youdon't eat dessert, you'll replace it with a healthier snack (which costs the same), which will bring you $20 of value each time you eat it.

Every dessert you eat instead of the healthy snack imposes health costs. This totals out to $10 in costs for the first dessert, $20 for the second, $30 for the third, and so on.

What is the optimal number of desserts to eat each week?