Confusion with Algebra (Substitution) I apologize for the title, I'm not sure what category this would fall under.
The advertisement read Buy $3$ tires at the regular price and get a fourth tire for only $3$ dollars. Carol paid $\$240$ for a set of $4$ tires. What is the regular price of a tire?
So I came up with $3x + 3 = 240$.
$\frac{240}{3} = 80$
$3 = 80$ does not make sense.
Why do I have to subtract the $3$ first? I was told that when using systems of equations I needed to use PEMDAS.

Your goal is to manipulate your equation (which you set up correctly) to get the x by itself.  And remember that you have to do the same thing to each side of the equals sign each step along the way.  
$$3x+3=240$$
Now, you can either subtract 3 from each side or divide the entirety of each side by 3.  I see now that @onetoinfinity has posted an answer that shows how to do this, so, see if that helps...
