The formula is called the “midpoint formula”. It looks like this
m=(x1+x2)/2 , (y1+y2)/2 where m means midpoint. In your case it looks like this.
If the runner moves at 6 miles per hour for 2 hours before the cyclist starts, the runner has a 12 mile lead at the beginning. If the cyclist is going at 16 miles per hour, he is overtaking the runner at 10 miles per hour, because 16-6=10. Then, the amount of time it takes the cyclist to go 2 miles in 10 miles per hour is the answer. this is 1/5 of an hour, or 12 minutes.