Final answer:
Goods X and Y are complements because the decrease in the cost and price of good X causes an increase in demand for good Y. This indicates that the goods are used together and that consumption of one enhances consumption of the other.
Step-by-step explanation:
When the cost of producing a good X decreases, leading to a reduced price per unit, and subsequently the demand for another good Y increases, this suggests that goods X and Y are complements. Complements are goods that are often used together; the consumption of one enhances the consumption of the other. Examples of complementary goods include coffee and sugar, printers and ink cartridges, or smartphones and phone cases.
In contrast, if goods X and Y were substitutes, a decrease in the price of good X would lead to an increase in its demand but a decrease in the demand for good Y. Substitutes are goods that can replace each other in use. An example would be butter and margarine; if butter becomes cheaper, people might buy less margarine.
Based on the described scenario, it is clear that goods X and Y are not substitutes but are indeed complements, as a reduction in the price of good X has led to a higher demand for good Y.