Find the midpoint of the line segment whose endpoints are (-2, 5) and (4, -9).

You just want to find the middle of the pair of x coordinates and the pair of y coordinates.

Or,

The number in the middle of -2 and 4, and also 5 and -9.

Number in between -2 and 4: The distance between them is 6, so the number must be 3 away from both of them. -2 + 3 = 1.

Number in between 5 and -9: The distance is 14. Number must be 7 away from both. -9 + 7 = -2

So the midpoint would be:

(1, -2)

No solution : there is no number of boxes that she bought