John Is Trying to Decide How to Divide His Time

Multiple Choice

John is trying to decide how to divide his time between his job as a stocker in the local grocery store, which pays $7 per hour for as many hours as he chooses to work, and cleaning windows for the businesses downtown. He makes $2 for every window he cleans. John is indifferent between the two tasks, and the number of windows he can clean depends on how many hours he spends cleaning in a day, as shown in the accompanying table.  
Should John spend a third hour cleaning windows?

A) Yes, because he would earn $28.
B) Yes, because the additional amount he would earn is $14, which is greater than his opportunity cost of $7.
C) No, because the additional amount he would earn is $6, which is less than his opportunity cost of $7.
D) Yes, because the additional amount he would earn is $6, which is better than earning nothing.