Descompunem numerele:
x23 cu bara deasupra = 100x + 20 + 3
23x cu bara deasupra = 200 + 30 + x
3x1 cu bara deasupra = 300 + 10x + 1
100x + 20 + 3 + 200 + 30 + 300 + 10x + 1 = 666
110x + 54 + 500 = 666
110x = 112
x = 112 : 110
x = 1,0(18)