Grade with Plus or Minus

The variable score is a test result from 0 to 100. Print the letter grade with a modifier. First decide the letter as usual: A for 90 and above, B for 80 to 89, C for 70 to 79, D for 60 to 69, F below 60. Then, for the letters B, C and D only, look at the last digit of the score (score % 10): 7 or more adds +, 2 or less adds -, anything else adds nothing. A and F never get a modifier. Build the result in a variable called grade and print it on its own.