The average is equal to the mean of the data set. It is the total of the data or numbers given divided by the ordinal unit of the data set. In this case, we are given with scores of 95, 92, and 89. To have an average of at least 93, the fourth score should be :
95 + 92 + 89 + x ≥ 93 * 4 where 4 is the number of data points.
x ≥ 96. Test score should be equal or greater than 96.