Answer:
the demand curve for blue shirts would shift
the blue shirt's demand curve
lower
lower
Explanation
Blue shirts and green shirts are substitute goods.
Substitute goods are goods that can be used in place of another good.
If the price of green shirts falls, green shirts become cheaper and the quantity demanded of green shirts increase.
As a result of the increase in demand for green shirts, the demand for blue shirts would fall. the would lead to a leftward shift of the demand curve. As a result equilibrium price and quantity would fall.
