3.
(15 1/3 - 8 5/18) * 2 4/7 : 6 1/21 - 2 5/8
15 1/3 - 8 5/18 = 46/3 - 149/18 = (276 - 149) / 18 = 127/18
127/18 * 2 4/7 = 127/18 * 18/7 = 127/7
127/7 : 6 1/21 = 127/7 : 127/21 = 127/7 * 21/127 = 3
3 - 2 5/8 = 3 - 21/8 = (24 - 21) / 8 = 3/8
4.
8,25 : 1,1 - (3 - 2,8 * 3/7) : 0,6
8,25 : 1,1 = 7,5
2,8 * 3/7 = 14/5 * 3/7 = 6/5
3 - 6/5 = (15 - 6) / 5 = 9/5 = 1,8
1,8 : 0,6 = 3
7,5 - 3 = 4,5