Simple...
you have: -3x+9y=-54
If you want to find the yi-intercept of this line you must first re-write it in y=mx+b form-->>
-3x+9y=-54
-3x+9y=-54
+3x +3x
9y=3x-54
Now divide by 9...
[tex] \frac{9y}{9} = \frac{3x-54}{9} [/tex]
y=[tex] \frac{1}{3} x-6[/tex]
As we can see the y-intercept is located at (0,-6).
Thus, your answer.