(5/6) (9/15) - (5/12) (4/15) = (5 9) / (6 15) - (5 4) / (12 15) = 45 / 90 - 20 / 180 = 1/2 - 1/9 = (9/18) - (2/18) = 7/18
(5/6) (9/15) - (5/12) (4/15)
= (5 9) / (6 15) - (5 4) / (12 15)
= 45 / 90 - 20 / 180
= 1/2 - 1/9
= (9/18) - (2/18)
= 7/18