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...

y=

As we can see the y-intercept is located at (0,-6).
Thus, your answer.