Solution: Since the coordinates of point A are -20 and point B are 100, the distance between point A and point B is 120, that is, 120 units. If ant P meets ant Q x seconds after leaving, ant Q also moves x seconds to meet ant P (because both ants leave at the same time).

Then you can make a formula.

6X+4X= 120

(Analysis) The speed of ant P is 6 units/second multiplied by time x seconds+the speed of ant Q is 4 units/second multiplied by time x seconds, which is equal to the total distance 120 units.

According to the above formula, X= 12 (seconds)

Then the distance that the ant P moves is 6 times 12=72 (unit).

100-72=28

The number corresponding to point C is 28.