4 - 7f = f - 12
Subtract f from both sides.
4 - 7f - f = -12
Subtract 4 from both sides.
-7f - f = -12 - 4
Simplify.
-8f = -16
Divide both sides by -8.
f = 2
To show your work, simply plug in the value of f into the original equation.
When f = 2, :
4 - 7f = f - 12
4 - 7(2) = (2) - 12
Simplify.
4 - 14 = 2 - 12
Simplify.
-12 = -12
So, f = 2
~Hope I helped!~