7a+(4+5a)=12a+4
The first step to this is to simplify both sides of the equation.
You have to combine all of the like terms first...
(7x + 5x) + (4) = 12x + 4
12x + 4 = 12x + 4
Now the second step is to subtract 12x from both sides....
12x + 4 = 12x + 4
-12x -12x
4 = 4
Now you will subtract four from both sides and get....
0=0
