I am having trouble with making bullets disappear at the left side of the world mainly because I can't get the exact coordinates. I can support code but I don't know what is needed.
If you use the normal world constructor ( 'WorldClassName(int, int, int)' ) and not the other one ( 'WorldClassName(int, int, int, boolean)" ), then your actor will never have a negative x-coordinate value. If you try to place or move your actor passed the left edge, it will be place at the left edge. In other words, its x-coordinate value will be zero and never go below it.