raising grades

Your task is to write a PHP script that reads grades from the file grades.txt, increments the grades by one and writes the incremented grades to the file results.txtand finally prints the grades from results.txt. If the grade is five, it won’t be incremented. The grades in grades.txt are each in its own row and the amount of digits in a grade may vary. The grades are between 0-5. The grades written in results.txt should each also be in their own rows.