how do i get one box to equal the total of that box times the locked column box

See I am a QA Supervisor on a mushroom farm and I am creating a spredsheet that I want to allow me to lock in certain product types and their weights then I want to be able to then add the number of boxes that product type that the picker picked and times it by the weight I have initially locked in

@Jamiesgirl: The question is unclear. Please write in complete sentences ending with “.”. Also, edit the question to show an example of what you want. And in the future, do not check community wiki. See guidelines for asking.