Write a function called letter_grade that takes a positive integer called score as its input argument and returns a letter grade according to the following scale: A: 91 and above; B: 81-90; C: 71-80; D: 61-70; F: below 61. Remember that to assign a letter to a variable, you need to put it in single quotes, as in: grade = 'A'.

function grade = letter_grade(score)
if score>=91
    grade = 'A';
elseif score>=81 && score<=90
    grade = 'B';
elseif score>=71 && score<=80
    grade = 'C';
elseif score>=61 && score<=70
    grade = 'D';
elseif score<61
    grade = 'F';
end