First we will assign the variables
second exam: x
third exam: y
Because the second score is 4 less than the third
x=y-4
with this information, we can rewrite
second exam: y-4
third exam: y
Now, we have this equation of average
(82+y+y-4)/3=72
(2y+78)/3=72
then we can clear y
2y+78=216
2y=216-78
2y=138
y=138/2
y=69
69 on the third exam
65 on the second exam