..................=13 11/28
1) 123 23/28 - 120 5/21=123 69/84 - 120 20/84=3 49/84=3 7/12
2) 4 2/7 - 3,4=4 2/7 - 3 2/5=4 10/35 - 3 14/35=31/35
3) 10,5 * 31/35=21/2 * 31/35=93/14=6 9/14
4) 12 - 6 9/14=5 5/14
5) 3 7/12 * 5 5/14 * 30/43=43/12 * 75/14 * 30/43=1125/84=13 33/8413 11/28