The equilibrium quantity of the good or service will decrease if demand decreases and supply increases.
When demand decreases, consumers want to buy less at every price level, which pushes the equilibrium quantity down. If supply increases at the same time, it means producers are supplying more of the good, which also tends to lower prices and can further decrease the equilibrium quantity, depending on the magnitudes of the shifts in demand and supply.
So, the correct response is:
demand decreases and supply increases.