Final answer:
To maximize the utility function U = C × T, Ria and Manuel should compare the marginal utility of cookies to the marginal utility of tea and adjust their consumption accordingly.
Step-by-step explanation:
To maximize the utility function U = C × T, where C is units of cookies consumed and T is units of tea consumed, Ria and Manuel should consume cookies and tea in a way that maximizes their total utility. They should choose a combination of cookies and tea that gives them the highest possible total utility. This can be done by comparing the marginal utility of cookies to the marginal utility of tea and adjusting the consumption of each until the marginal utilities are equal.
For example, if the marginal utility of cookies is higher than the marginal utility of tea, Ria and Manuel should consume more cookies and less tea to increase their total utility. On the other hand, if the marginal utility of tea is higher, they should consume more tea and fewer cookies.
By balancing the consumption of cookies and tea based on their marginal utilities, Ria and Manuel can maximize their utility function U = C × T.