We can write this as follows :
-12 - [- 4 ] - 6- [ - 8 ] = -6
A negative outside any parentheses or bracket changes the sign on the thing inside and we can "drop" the negative outside
So we really have
-12 + 4 - 6 + 8 =
- 8 - 6 + 8 =
-8 + 8 - 6 =
0 - 6 =
- 6
