Final answer:
The price of X at point D on the demand curve is not specified in the given data. The Marginal Rate of Substitution (MRS) at point B on the indifference curve cannot be quantified without further information, and the consumer's income at point B cannot be determined without knowing the budget constraint or prices of goods.
Step-by-step explanation:
Responding to the student's question, to determine the price of X at point D on the demand curve for X, we can refer to the provided equilibrium analysis. Since it is not explicitly stated in this context, we can't provide the exact price without further information. For part c, the Marginal Rate of Substitution (MRS) at point B on indifference curve II would represent the rate at which a consumer is willing to give up some amount of doughnuts to obtain an additional book, maintaining the same level of utility.
However, without a graphical representation or additional numerical details, it is impossible to quantify this rate. Finally, regarding part d, we cannot provide a precise income at point B without knowing Lilly's budget constraint or additional context that relates quantities of books and doughnuts to their respective prices.