Suppose the quantity demanded of good X (Q) depends only on the price of good X (P), monthly income (M), and the price of a related good R (PR): Qd=30,500-1,000P+0.25M+5PR Good Ra for good X. All else constant, a 3 decrease in PR will cause quantity demanded of good X to by units.
a. substitute; increase; 0.75
b. substitute; decrease; 15
c. substitute; decrease, 3
d. complement; increase; 3