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.  
What is the lowest price per window that John would be willing to accept to spend 4 hours per day cleaning windows?

A) $7
B) $2
C) $3.50
D) $11