Answer:
The overall final score of the student is 75.4, in letter scale, a C.
Explanation:
Assuming that numbers are repeated (1010% means 10% and so on).
To find his overall final score, we have to take into account that it is a weighted average.
A weighted average is one where each score (x) has a specific weighing, for example, midterm's weighing in this case is 10%. If we add all weighings, we should get 100% (it is the case). The formula is:

With our data:

As the mean is 75.4, higher than 70 but lower than 80, he earned a letter grade of C.