6
7351 = 7*3*5*1 = 105 = ..5 439=4*3*9 = ..8; 12456 =1*2*3*4*5*6=..0 2*4*6*2 = ..6
If 5 + 4 => 9 3 + 5 => 9 9 + 1 => 9 1 + 6 => 8 4 + 2 => 8 1 + 7 => 7 5 + 6 => 6 3 + 7 => 3 7 + 0 => 0 Then 8 – 1 => ??