How do I make y the subject of an equation? For example in 9x = 3x + 2y.

There are several ways we can rearrange algebraic formulae in order to change the subject. Changing the subject basically means changing the variable (letter) that we are trying to find out, so getting the letter on its own on the other side of the equals sign. In this case we want y on its own. One way we can do this is by balancing both sides of the equation, remember whatever we do to one side of the equal sign, we have to do to the other.As we are trying to get y on its own on the right hand side, let's try and get rid of the term on the right that doesn't have y in it. This term is a positive 3x. If we have +3x on the right side, how could we get rid of it (make this =0)? We could subtract 3x. Remember, whatever we do to one side we do to the other to make sure our equation is balanced. So we have to subtract 3x from the left hand side as well, now we have 6x = 2y. We want y on its own, but there is a 2 in front of it, what does this mean? This means 2 multiplied by y. If we have multiplied y by 2, how could we get back to our original y? We would have to do the opposite and divide by 2. If we divide 2y by 2 to get y, we have to do the same to the left hand side and divide that by 2. This gives us 3x = y, which is the same as y = 3x. Now we have made y the subject of our equation.