2/15 у +3/4 = 5/6
2/15 у = 5/6 -3/4
2/15 у = (10-9)/12
2/15 у = 1/12
у= 1/12 : 2/15 = 1/12 * 15/2 = 15/24
у= 5/8
=============
2/15 * 5/8 + 3/4 = 5/6
(1*1)/(3*4) +3/4=5/6
1/12 + 3/4 = 5/6
1/12 +9/12 = 5/6
10/12 = 5/6
5/6=5/6
5/8 m - 7/12 m +5/6 m = 1/4
(5/8 -7/12 +5/6 ) m = 1/4
(15/24 - 14/24 + 20/24 ) m = 1/4
21/24 m = 1/4
7/8 m = 1/4
m = 1/4 : 7/8 = 1/4 * 8/7 = (1*2) / (1*7)
m= 2/7
============
5/8 *2/7 - 7/12 * 2/7 + 5/6 * 2/7 =1/4
5/28 - 1/6 + 5/21 = 1/4
15/84 - 14/84 + 20/84 = 1/4
21/84 = 1/4
1/4 = 1/4