3 * 1/21 + 2* 1/14 * (1, 6 - 6, 4) : 0, 8 = - 5/7
1) 1.6 - 6.4 = -4.8
2) 3 * 1/21 = 1/7
3) 2 * 1/14 = 1/7
4) 1/7 * - 4.8 = - 24/35
5) -24/35: 0,8 = -24/35 : 8/10 = - 24/35* 10/8 = -6/7
6) 1/7 + (- 6/7) = 1/7 - 6/7 = -5/7
