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.

$\backslash$table$[[\backslash$table$[[$Time cleaning$],[$windows$],[($hours$/$day$)]],\backslash$table$[[$Total number of$],[$windows cleaned$]]],[0,0],[1,7],[2,11],[3,14],[4,16],[5,17]]$

What is John's opportunity cost of cleaning windows for an hour?

Multiple Choice

$$8$