Lpp Problem for optimizing workers in a process

Scenario : You are an Inbound Manager of a Distribution Center operated by a Third Party Logistics Company (3PL) for a large retailer. You need to complete 300 orders in 90 mins by completing 3 processes which take the respective time for each order. (i) - Sorting - 4 mins (ii) - Checking - 4 mins (iii) - Packing - 3 mins As a rule , each worker cannot work on multiple processes for the same order. i.e A worker A working on Sorting of Order 1 cannot work on Packing of Order 1. But he can work on Packing/Checking of any other order. What is the least number of people required to complete the order.