(6,5 - 1,3х) * 4/13 = (0,8 - 3х) : 6/7
6 1/2 * 4/13 - 1 3/10х * 4/13 = 4/5 * 7/6 - 3х * 7/6
7/2 * 4/13 - 13/10х * 4/13 = 14/15 - 7/2х
14/13 - 2/5х + 7/2х = 14/15
35/10х - 4/10х = 14/15 - 14/13
31/10х = 182/195 - 210/195
31/10х = -28/195
х = -28/195 : 31/10
х = -28/195 * 10/31
х = - 56/1209