You may want to review solving ordinary linear equations first.

Sometimes, linear equations have more than one variable. That's
okay; you just need to know which one we're interested in. When
you're given a problem, it should say to solve “for”
some variable. If you're told to solve 3*x* + 4*y*
− 4 = 2*x* − 1 for *y*, say, then that means
that you need to find what values of *y* make the equation
right. The answer will in general depend on *x*. That's okay
— you're allowed to have letters in your answer. The one
letter that you *aren't* allowed to have in your answer is
the letter you were asked to solve for.

You do these problems the same way you solved linear equations
with just one variable in them, except you treat the other letters
the same as you would numbers. You might have to simplify your
answer at the end. In our example, both sides are already
simplified, and *y* (the letter we're solving for) is only on
one side. However, there's stuff being added and subtracted on the
side where *y* is. So we need to subtract 3*x* from both
sides and to add 4 to both sides. This gives us 4*y* =
−*x* + 3. Now we divide both sides by 4 (the
number *y* is being multiplied by) and get *y* =
(−*x* + 3) / 4, which simplifies to
−(1 ⁄ 4)*x* +
3 ⁄ 4, so that's our answer.