Create a method get_grade that accepts an average in the class and returns the letter grade as a String. It should only return one of 'A', 'B', 'C', etc. Don't worry about + and - grades. For example, get_grade(89) # => returns "B", *not* "B+" get_grade(70) # => returns "C"

Calculate a letter grade

def get_grade(num)
  if num >= 90
    return "A"
  end

  if num >= 80 && num <= 89
    return "B"
  end

  if num >= 70 && num <= 79
    return "C"
  end
  
  if num >= 60 && num <= 69
    return "D"
  end
  
  if num <= 59
    return "F"
  end
end