An increase in the price of movie theater tickets (a substitute for DVD rentals) will cause the demand curve for DVD rentals to shift to the right. An increase in the wages paid to DVD rental store clerks (an increase in the cost of a factor of production) shifts the supply curve to the left. Each event taken separately causes equilibrium price to rise. Whether equilibrium quantity will be higher or lower depends on which curve shifted more.
If the demand curve shifted more, then the equilibrium quantity of DVD rentals will rise [Panel (a)].
If the supply curve shifted more, then the equilibrium quantity of DVD rentals will fall [Panel (b)].
If the curves shifted by the same amount, then the equilibrium quantity of DVD rentals would not change [Panel (c)].