add user page to a hosted website

I have a website that my company hosted using hubspot.. now the guy who made it is gone..

Currently all the code is in the front end which i think was made by using the CMS tool of hubspot.

What i need to do is add another page to this website which has my code and also has a backend code in it.

Plese help 开发者_运维知识库me how do i proceed.. i am currently working with asp.net and C#...

So please tell me which language i should chose to do the backend coding.. the code i plan to write is not that complex.. i just need to get a value for the user using a textbox, multiply with a number and display/email it back.

your requirements sound quite simple - I would try and maintain an approach which is consistent with the existing architecture - ie client-side HTML/javascript (by the sound of it). You don't really need to use ASP.NET to capture user input and display it in the way you describe. You could do that just with a few lines of Javascript. Emailing might be a bit more complicated. The simplest approach would be to use a mailto link.