Letter grades, whereas other courses assign a percentage between 0 and 100. Still others assign a pass/fail grade. Write an interface named Grade. The toPercent method returns the grade as an integer percentage between 0 and 100 percent. The toString method prints the grade in its "native" format (a percentage, a letter grade, or either "Pass" or "Fail"). The isPass method returns true for a passing grade, false otherwise. The include In Average returns true for letter and numeric grades, but false for pass/fail grades.