1.
45 : 3 6/13 - 13,6 + 1 3/8 =
45 : 45/13 - 13,6 + 11/8 =
45 * 13/45 - 136/10 + 11/8 =
13 - 136/10 + 11/8 =
520/40 - 544/40 + 55/40 = 31/40,
3.
2,6х-0,75 = 0,9х-35,6,
2,6х-0,9х = -35,6+0,75,
1,7х = -34,85,
х = -20,5,
4.
6 3/7 : 1 6/7 = 4,5 : х,
х = (1 6/7 * 4,5) / 6 3/7,
х = (13/7*45/10) / 45/7,
х = 13/7 * 45/10 * 7/45,
х = 13/10,
х = 1 3/10 (или 1,3)