3x + y = 1 | Original equation
3x + 6 - 4x = 1 | The expression in the second equation is substituted for y in the first expression.
3x - 4x + 6 = 1 | Rearrange order of operations (commutative property)
-1x + 6 = 1 | Added like terms
b: -x + 6 = 1 | Final equation
