Answer:
51 or above
Explanation:
He already averages more then 78. But he at least needs a 51 in order for him to average 78. For him to get more than that he just needs a 52 or higher.
78 x 5 = 390
95 + 92 + 84 + 68 = 339
339/ 4 = 84.75 ( just to let you know the average before #5 )
390 - 339 = 51
51 is that last score needed