At a make-to-order hamburger shop, there is one worker who cooks patties, two workers who assemble burgers, and one cashier. The oven can cook patties in 4 minutes and the oven can cook up to 20 patties at one time. Each burger assembler can assemble a burger in 30 seconds. It takes the cashier 6 seconds to collect payment.

a) What is the capacity of the hamburger restaurant in customers per minute? What is the bottleneck?
b) If one more burger assembler is hired, what is the capacity of the burger store? What is the bottleneck?
c) Disregarding part b), if the restaurant buys another oven, what is the capacity of the restaurant? What is the bottleneck?