An average is the sum of the scores divided by the number of games played.
For her average to be 91 after 4 games the total of the scores needs to be 91 x 4 = 364
To find what her 4th score needs to be subtract her first 3 scores from 364
364 - 108 - 72 - 95 = 89
Her 4th game needs to be 89
