Puzzle ZCXA 

Workings

Hint
Try working backwards.

Answer
148.

148 x 6 = 888.

The easiest way is to divide successive 8's by 6 until you get an integer:
  8 ÷ 6 = 1.3333
 88 ÷ 6 = 14.666
888 ÷ 6 = 148