9/35 * 9/14 + 3/14 * 9/14 - 5/21 * 9/14 = (9/35 * 9 + 3/14 * 9 - 5/21 * 9) / 14

= (81/35 + 27/14 - 45/21) / 14 = (81 + 189 - 135) / 35 / 14 = 135 / 35 / 14 = 9 / 14.