Although the points do not sit exactly on integer coordinates, we can round their coordinates and say that
Now, remember that the first coordinate represents the number of events, and the second coordinate represents the number of stamps. So, if we want the number of events to be four times the number of stamps, we need a point whose first coordinate is four times the second.
This is the case for point C, because its first coordinate is about 20, and its second coordinate is about 5, and 20 is four times 5.