First add 1 to 1 so they cancel, so 4b=-13
Whatever you do to one side you have to do to the other, so add 1 to -13 so 4b=-12
Now divide 4b by 4 to be left with b so b=-12
But remeber whatever you do to one side you must do to the other, so divide -12 by 4 as well
So after doing all that you end up with, b=-3
But let's check just to make sure, 4*-3=-12 -12-1=-13
So the answer is correct.