A supermarket can employ either cashiers (labor, L) or machines (capital, k) to operate it's checkout lines. Cashiers (L) can perform checkouts at a constant rate of 20 customers per hour, while machines (k) performs them at a constant rate of 60 per hour, or: y(k,L) = 20L +60k. The cost of L is w = 15 per hour, while the cost of k is r = 50 per hour. How much L and k should the supermarket employ each hour to service its 300 customers per hour at the lowest cost?