To find average, add up the values given and then divide that number by the amount of values that you added to make the larger number.
For example:
If he ran -8 yards first and -6 yards second and they are asking you to find the average, add -8 and -6. You get -14. If you then divide by 2 because you added 2 numbers together, you end up with -7.
Hope this helps!