In Azure DevOps I'm adding some fields on a task and now I'll do some calculations with them. For example if I enter in field A 10 and in the field B 50, field C must be equal to 15, calculated using this formula: A + A * B / 100.

How can I do that? I've looked for extensions but didn't find anything free. I've also asked it on the developer community from Visual Studio but after 1 month I've no answer or comment.