a boy has an average score of 5.375 for 4 Indonesian language exams. then the boy joins one remedial exam. to reach the mean at least 6.00, what is the minimum

5,375 for 4 exam. It means his total score is
4(5,375) = 21,5

How to make the mean at least 6,00 for 5 exams (4 exams before and a remedial after it) so the total score should be 30,00.
We can know his score for last exam by :
5(6,00) - 4(5,375)
= 30,00 - 21,50
= 8,50

So, he must get at least 8,50 in remidial exam to get the mean 6,00