Robert and his roommate bake cakes. When they receive an order over the internet, Robert mixes cake batter according to the order (takes 6 minutes). He pours the batter into a baking pan that holds 1 cake (2 minutes). Johnny then puts the cake pan in the oven and sets a timer (1 minute). Cakes bake in the oven for 9 minutes and then are cooled outside the oven on a rack for 5 minutes. Finally the Johnny takes 2 minutes to box the cake and then takes the payment from the arriving customer (1 minute).

Each cake order is composed of a two tier cake (2 cakes). Also Robert and his roommate can only perform their assigned activities and cannot perform the other's. The mixing bowl can hold batter for two cakes at one time, assume the oven can only hold one cake pan at a time. As mentioned above, pouring batter into each pan takes 2 minutes, both cakes must be cooled before boxing, and each cake is put into the box separately one on top of the other.

1. Determine theoretical flow time from the order thru payment, no waiting over the entire process.

The answer is 36 minutes

This is what I have but if I use the same scenario I cannot get the correct answers for numbers 2 and 3: