Answer: 97
Explanation:
Average: All the numbers added divided by the number of numbers
Start adding the smallest grade in her notes: 87+96+81+89+81= 434/5= 86.8
Keep adding 1 to the last grade until you find a number that gives us an average of 90.
87+96+81+89+97+ 450
Then divide it by the amount of grades
450/5= 90