Please help me to check what did I do wrong here, thank you! it's a matlab question

Question 2: consider the following scheme which maps an integer quiz grade to a corresponding letter grade: 9 or 10 is an A 8 is a 'B' 7 is a 'C' 6 is a 'D' Anything below 6 is an 'F' Write a function called letgrade which receives an integer quiz grade and returns a corresponding letter as per the scheme above. Also the function returns the letter X if the quiz grade is not valid. This can be implemented with if else statements