Explanation

To find the Highest Common Factor (HCF), list the factors of each number:

135: 1, 3, 5, 9, 15, 27, 45, 135

540: 1, 2, 3, 4, 5, 6, 9, 10, 12, 15, 18, 20, 27, 30, 36, 45, 54, 60, 90, 108, 135, 180, 270, 540

675: 1, 3, 5, 9, 15, 25, 27, 45, 75, 135, 225, 675

765: 1, 3, 5, 9, 15, 17, 27, 45, 51, 85, 135, 153, 255, 765

The highest common factor among these numbers is: 45.