Simple Google Chrome extension

Hello, I am looking for someone being able to make a Google Chrome extension. The extension will be used for personal use by 2 people. It will be used on the mac version of Google Chrome and the Windows version of Google chrome. The extension has to take 3 fields on a certain page whenever accessed and make a calculation I have already written (simple division and multiplication) on the number and display 2 sentences on the bottom right of the screen whenever the page is accessed and the numbers are displayed. I need the 2 bits of information to be only displayed whenever the page is accessed and whenever certain values are generated.