If you would like to simplify the expression (x - 8y) - (2x - 4y), you can do this using the following steps:
(x - 8y) - (2x - 4y) = x - 8y - 2x + 4y = -x - 4y
ax + by = -x - 4y
a = -1
b = -4
The value of b would be -4.
If you would like to simplify the expression (4x - 6) - (3x + 6), you can do this using the following steps:
(4x - 6) - (3x + 6) = 4x - 6 - 3x - 6 = x - 12
The correct result would be x - 12.