The median is the middle score, it is also the average of the two middle scores when total number is even.
original 3 scores: 89, 90, 95 ----> median = 90
with final score: 89,90,X,95 ----> median = 91.5
(90+x)/2 = 91.5
90+x = 183
x = 93
Final score was a 93.