There is no Junk Penalty on a mission Model like the white Plastic Bags. Mission Models may be stranded anywhere out in the field with no Penalty.
The Interruption and Junk Penalties are assessed by taking one of the referee's Black Bars and placing it on the mat. The point value for that is determined by mission M04. The score for each penalty Black Bar is -8. (As others have noted, this results in a net change of -16 in the score, since the bar would have been worth +8 before the Penalty,)
Virginia-DC FLL Referee Advisor