3/7 - 16/21 = 9/21 - 16/21 = -7/21
11/15 + 0,3 = 11/15 + 3/10 = 22/30 + 9/30 = 31/30 = 1 1/30
- 7/21 * 2 1/7 = - 7/12 * 15/7(Здесь сократить 7 на 1, а 12 и 15 на 3) = -5/4 = -1 1/4
1 1/30 / 12 2/5 = 31/30 * 62/5 = 31/30 * 5/ 62( 31 и 62 на 31, а 30 и 5 на 5) = 1/12
-1 1/4 + 1/12 = -1 3/12 + 1/12 = -1 2/12 = -1 1/6
Держи)))