Move all terms not containing b to the right side of the equation.
Add 4 to both sides of the equation.
Add 8 and 4.
Multiply each term in -b=12 by -1
Multiply each term in -b=12 by -1.
Multiply -1 by -1.
Multiply b by 1.
Multiply 12 by -1.
Solve for b -4-b=8