(у + 30) = 160 : 20
у + 30 = 8
у = 8 - 30
у = - 22
-------------------------------
16 - х = 216 : 18
16 - х = 12
х = 16 - 12
х = 4
-------------------------------
8х + 91 = 21 * 7
8х + 91 = 147
8х = 147 - 91
8х = 56
х = 7
------------------------------
5у + 21у + 54 = 106
26у = 106 - 54
26у = 52
у = 2
------------------------------
8х + 52х + 128 = 308
60х = 308 - 128
60х = 180
х = 3
-----------------------------
55х - 155 - 9х = 121
46х = 121 + 155
46х = 276
х = 6