12x-x-55=0
11x - 55 = 0
11x = 55
x = 55 : 11
x = 5
-----------------------------
12 * 5 - 5 -55 = 0
60 - 5 - 55 = 0
55-55=0
2+6a+4a=92
2 + 10a = 92
10a = 92 -2
10a = 90
a = 90 : 10
a = 9
-----------------------------
2 + 6*9 + 4*9 = 92
2 + 54 + 36 = 92
2 + 90 = 92
92 = 92