Answer:
c. equilibrium quantity decreases from 15 to 13
Explanation:
When demand schedule is D1 and supply schedule is S1,the equilbrium is established at 13 units and price is $6.(quantity demanded = quantity supplied)
Initially when demand schedule was D2 and supply schedule was S1, equilibrium was established at 15 units and price = $8.
Equilibrium quantity decreases from 15 to 13