Customers arrive at this process in the following way: Every $240$ secs two customers arrive at M$1$ starting from time $0$ and every $240$ secs one customer arrives starting from time $100.$ Once a customer arrives at stage $2,$ if both servers are empty, the customer is served at the server with lower processing time. Fill in the Gantt chart. Each grid in the following chart represents $20$ sec$.$ You can extend the below chart as needed.