What is the inverse equation of the function, y = 3x - 6?
y -1 = 3x + 6
x -1 = 3y - 6
y -1= x+6/3
y -1 = 1/3x + 6

on the third answer the / means dividing

The best answer (and only correct answer) among the answer choices given is:

                    [C]:    y⁻¹ = (x+6) / 3  .

Explanation:

 Given the original function:  y = 3x - 6 ;

To find the "inverse equation" of said function; we change the "x" to a y"; and the "y" to an "x"; and rewrite:

x = 3y − 6 ; 

Now, rewrite in "slope-intercept form" ; or y = mx + b ;
     that is, with y as "single, isolated" variable on the left-hand side of the equation (with an "implied coefficient of positive one", only);  then an "equal sign, then "mx + b" ; in which: "m" is the coefficient of the variable, "x"; and in which "m" refers to the "slope";  and "b" refers to the 'y-intercept".

So,we have the inverse function: 
 
      x = 3y − 6  ;  we want to write in slope-intercept form; 

Add   "6" to each side of the equation:

     x + 6 = 3y − 6 + 6 ; 

 x + 6 = 3y ;  

 ↔ Rewrite as:   3y = x + 6 ; 

 Divide EACH side of the equation by "3" ; to isolate "y" one side of the equation; specifically, the left-hand side of equation; and to write in "slope-intercept form:

              3y / 3 = (x + 6) / 3  ;

   to get:

                  y = (x + 6) / 3 ; 

                 y = (x/3)  + (6/3) ;

                y = (x/3 ) + 2 ;

or;  write as: y = (1/3)x + 2 ;

Now, let us examine the answer choices given:

Note that all the answer choices begin with "y-1" ;
    (except "answer choice: [B]" , which begins with "x-1").  This seems confusing; however, in reality, this does not mean, "y minus 1"; or "x minus 1".  Rather, it mean y⁻¹  or x⁻¹  as notation for the "inverse" (not to be confused with the exponent notation.  The confusion stems from the fact that it can be difficult to make such notations on the "" system.

That being said, we can write the aforementioned "rewritten equations" (see above in THIS VERY ANSWER) as:

y⁻¹ = (x + 6) / 3 ; 

                 y⁻¹ = (x/3)  + (6/3) ;

                y⁻¹ = (x/3 ) + 2 ;

or;  write as: y⁻¹ = (1/3)x + 2 

That being said:

The best answer (and only correct answer) among the answer choices given is:  Answer choice: [C]:  y⁻¹ = (x+6) / 3  .

It would take her 20 minutes.