Hyper link with property value as form field

Hi,

I have a form with two fields

One is a text field AA where user enters a text "PC-1234"

Then the other field shall after save be a hyperlink field containing "the web url"+field AA value

Http://webpageABC.com/PC1234

so user can click on the hyperlink and have the web page opened in a new window

I've been looking around in some old post's but not been able to solve it

Please help

//Mikael