А) 1/6 y + 5/12 y = 8,4 Б)1 13/15 *

1) 1/6у + 5/12у = 8,4;

2/12у + 5/12у = 8,4;

7/12у = 8,4;

у = 8,4 : 7/12;

у = 84/10 * 12/7;

у = (7 * 12 * 2 * 6)/(2 * 5 * 7);

у = (12 * 6)/5;

у = 72/5;

у = 14 2/5.

2) 1 13/15 * (4 1/6 - х) * 14 8/9 = 1 1/2;

(4 1/6 - х) * 14 8/9 = 1 1/2 : 1 13/15;

(4 1/6 - х) * 14 8/9 = 3/2 * 15/28;

(4 1/6 - х) * 14 8/9 = 45/56;

4 1/6 - х = 45/56 : 14 8/9;

4 1/6 - х = 45/56 : (14 * 9 + 8)/9;

4 1/6 - х = 45/56 : 134/9;

4 1/6 - х = 45/56 * 9/134;

4 1/6 - х = (45 * 9)/(56 * 134);

4 1/6 - х = 405/7504;

4 1/6 - 405/7504 = х;

х = 4 + 7504/45024 - 2430/45024;

х = 4 5074/45024;

х = 4 2537/22512.