The answer is c. uncertain;decreases.

This would make the price of peanut butter uncertain and the quantity demanded for peanut butter decreases.

The price is uncertain because we don't know whether the price changes or stays the same. This happens when the supply and demand of the decreases at the same time and we are not sure to what extent. The supply and demand curve shifts to the left when they decrease.

There are three cases when supply and demand curve shifts simultaneously:

• One is where the price stays the same after the shift when both the supply curve and demand shifts at the same value.
• The supply curve shifts with a small amount to the left. This lowers the new price.
• The supply curve shift at a great amount to the left, This increases the new price.

Based from our question, the data did not say to what extent the price of peanuts and jelly rises. Therefore, the price of the peanut butter is uncertain.

The quantity demanded for peanut butter decreases. Based from the theory of demand, when the price increases, the quantity demanded decreases. Here, the price of the peanuts and jelly rises which lead to a lower quantity demand. There are two reasons for the theory behind the law of demand:

• The consumer prefers to buy the substituted goods over the higher price goods since the substituted goods offer the same satisfaction or utility from the higher price goods.
• The law of diminishing marginal utility occurs. When people consumes the same product over time, the additional satisfaction received decreases as the same amount of goods consumed increases.
• Please see the attached file for the complete solution