Answer:
87
Explanation:
To find the mean, add up all her grades for the 3 trimesters, and then divide by the number of grades.
Total of her Grades
Add up all her grades
84+87+90
261
Divide
Then, divide the total of her grades by the number of grades, which is 3.
261/3
87
So, the mean for her trimester grades is 87