Answer:
The owner makes $2 in sales per customer
Note: The "Amount of sales" label of the question is phrased poorly. s could be better labeled "profit from sales" or at least "Amount made from sales", etc.
Explanation:
If you logically think about how the answer (now that you know it) relates to the question, it should make simple sense.
i.e. if you consider the first column where $24 is made from 12 customers, and divide the $24 made by the 12 customers, you'll see that each customer spends $2.