You work in a fast$-$food restaurant. For the lunch rush, the cooks make five versions of each sandwich, placed in horizontal stacks. When there is only one sandwich left, the cashier puts a red sticky note on the top of the stack. This signals the cooks to make five new sandwiches. Some sandwiches sell out very quickly, while others take more time. What type of system is this?

an empirical system

a kanban system

a push system

a scrum system