Suppose Jaime and Cersei, two residents of the Kingdom of Westeros, divide their time between making daggers and shields. Jamie can either produce 8 daggers or 2 shields each week, while Cersei can either produce 5 daggers or 10 shields each week. Both Jaime and Cersei work 50 weeks per year. The accompanying figure shows their annual joint production possibilities curve. What is the slope of the production possibilities curve at point Z?.