Please show work when determining answer

Consider a batch process with two stations. Each station can handle a batch size of up to 100 units. Station 1 has a processing time of 2 minutes per unit, and no setup time. Station 2 has a setup time of 20 minutes per batch, and a processing time of 1 minute per unit. Processing units for a batch in Station 2 may only start when all the units in the same batch have been processed in Station 1. In contrast, set up for a batch in Station 2 may begin before that time. a) Of the above, what batch size is optimal in terms of minimizing the order flow time? a. 100 units b. 50 units c. 20 units d. 10 units