<h3>Answer: 15</h3>
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Explanation:
Extend the given line out as far as you can. I have done so using a red line in the attached image below.
Then move to "3" on the horizontal x axis. Draw a line straight up until you hit the red line. I use a green arrow to show this. You'll hit the blue point on the diagram. From there, move horizontally until you hit the y axis. You should land on y = 15. This shows the blue points coordinates are (3, 15)
x = 3 means three boxes contain a total of y = 15 chocolates.
note: the slope is 5 which represents the amount of chocolates in one box.