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.