How to create a web page that calculate and update users in same session

I have a programming assignment challenge and would like to get advice on how to start this.

A calculator website which logs calculations as they happen and shares those calculations with everyone connected to the website. For example, user A and user B go to your site at the same time. User A calculates "5 + 5", which equals "10". This is logged below the calculator as "5+5 = 10". User B is updated about this calculation right after user A posts it. Now, user B calculates "3x_4". This calculates to 12 and displays "3x_4=12" right below the prior calculation. User A sees this update immediately after user B posts it. Results should remain between sessions. Only show the last 10 calculations descending from most recent to oldest. Once the calculator is completed, send me the URL for your application.