20/51 / 15/68 + 0,6 * 1 7/18 = 16/9 + 6/10 * 25/18 = 16/9 + 5/6 = 32/18 + 15/18 =
47/18 = 2 11/18
3 1/3 / (7 / 5 1/4) - 1 7/12 = 10/3 / (7 / 21/4) - 19/12 = 10/3 / 4/3 = 5/2 - 19/12 =
30/12 - 19/12 = 11/12
(9 5/12 - 3 3/5 - 2 1/3) / 3 1/15 = (113/12 - 18/5 - 7/3) / 46/15 =
(565/60 - 216/60 - 140/60) / 46/15 = 209/60 / 46/15 = 209/184 = 1 125/184