1)1-x=26/31,2)(х-6 5/12):5/8=4

1) 1-х = 26/31
х = (26/31 - 1)/ -1 = (26/31-31/31)/-1 = (-5/31)/-1 = 5/31

2)(х-6 5/12) / 5/8 =4
(х-6 5/12) * 8/5 = 4
8/5 * х - 77/12 * 8/5 = 4
8/5* х = 4 + 10 4/15
х = 14 4/15 : 8/5 = 8 11/12