John Is Trying to Decide How to Divide His Time

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 table below: $$\begin{array} { | l | l | } \hline \begin{array} { l } \text { Cleaning time } \\\text { (hr/day) }\end{array} & \begin{array} { l } \text { Total numbers of } \\\text { windows cleaned }\end{array} \\\hline 0 & 0 \\\hline 1 & 7 \\\hline 2 & 11 \\\hline 3 & 14 \\\hline 4 & 16 \\\hline 5 & 17 \\\hline\end{array}$$
The first hour John spends cleaning windows costs him ________ that he could have earned in the grocery store.

A) $2
B) $7
C) $14
D) $18