Arrange the equations in the correct sequence to find the inverse of f(x)=y=x-4/33-x ?

equations: (only 6 out of the 9 equations are used)

1) 33x - xy = y - 4

2) 33x + 4 = y(1 + x)

3) 33x - xy = y + 4

4) 33x + 4 = y + xy

5) y = f^-1(x) = 1+x / 33x+4

6) 33x - xy = y+4

7) x = y-4 / 33-y

8) y = f^-1(x) = 33x+4 / 1+x

9) x(33 - y) = y-4

To find the inverse of the function, first is to replace every x with a y and all y with x's. 
That is, 
                          x = y-4/33-y    (Equation no. 7)
We solve y of the equation above by the steps below. 
                          x(33 - y) = y - 4      (Equation no. 9)
                          33x - xy = y - 4         (Equation no. 1)
                          33x + 4 = y + xy       (Equation no. 4)
                         33x + 4 = y (1 + x)     (Equation no. 2)
   Then, lastly,
                          y = f⁻¹(x) = (33x + 4)/(1 + x) (Equation no. 8)

Therefore, the arrangement of the equations is Equations 7, 9, 1, 4, 2, and 8.
                          

The answer is 30 minutes to an hour