How to make a nested IF formula easier to read

Nested IF function example

Write a nested IF function in cell D3 that assigns a grade of A for scores between 90 and 100, a grade of B for scores between 80 and 89, a grade of C for scores between 70 and 79, and a grade of F for scores below 70. (Hint: Search in Help for nested IF when constructing your function.) Copy this function to cells D4:D19.2. Calculate the average grade in cell B21. In cells C21 and D21, use a formula to determine whether the average grade is a passing grade, and the overall grade achieved by the