1) 18/х = 9, х = 18 : 9, х = 2
2) х/6 = 4 , х = 4 · 6, х = 24
3) 5/7 + 9/х = 7/8,
9/х = 7/8 - 5/9,
9/х = 63/72 - 40/72,
9/х = 23/72,
х = 9 : 23/72,
х = 9/1 · 72/23
х = 648/23 = 28 целых 4/23
4) 11/18 - 4/9 - 1/х = 0
11/18 - 8/18 - 1/х = 0
3/18 - 1/х = 0
1/6 - 1/х = 0
х = 6