$1.$ The demand for good X is given by

Research shows that the prices of related goods are given by $=$ $$5,900$ and $=$ $$90,$ while the average income of individuals consuming this product is M $=$ $$55,000.$

a$.$ Indicate whether goods Y and Z are substitutes or complements for good X$.$

The Pz is $-8,$ which indicates that it is negative. This means that if the price of good Z $($Pz$)$ increases, the quantity of good X $($Px$)$ decreases. Their behavior suggests that they are complementary since the increase in one causes the fall of the other.

b$.$ Is X an inferior or a normal good?

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c$.$ How many units of good X will be purchased when $=$ $$4,910?$