(7,8 - 3,2х) * 5/6 = (1,2 - 4х) : 8/15
7,8*5/6 - 3,2х* 5/6 = (1,2 - 4х)*15/8
1,3*5-1,6х*5/3=1,2*15/8-4х*15/8
6,5-8/3х=0,15*15-х*15/2
6,5-8/3х=2,25-15/2х
-8/3х+15/2х=2,25-6,5
-16/6х+45/6х=-4,25
29/6х=-4,25
х=-4,25:29/6
х=-4,25*6/29
х=-25,5/29
х=-255/290
х=-51/58