If you would like to simplify -4 * (7x - 3y - z) - 6 - (-6) * (9x - z + 2), you can do this using the following steps:
-4 * (7x - 3y - z) - 6 - (-6) * (9x - z + 2) = -4 * 7x + 4 * 3y + 4z - 6 - (-6 * 9x + 6z - 6 * 2) = -28x + 12y + 4z - 6 - (-54x + 6z - 12) = -28x + 12y + 4z - 6 + 54x - 6z + 12 = -28x + 54x + 12y + 4z - 6z + 12 - 6 = 26x + 12y - 2z + 6
The correct result would be 26x + 12y - 2z + 6.