This is a very simple project that you should be able to do with your eyes closed if you know what you're doing!
I have a functional php form that does some calculations and returns the results. (screenshot attached)
All you need to do is to write a few lines of JS or Ajax to make it work without page refresh. (JQuery is ok too) In other words, the form should be functional as it is for users who have JS disabled, but if JS is enabled it should be handled without refreshing the page.
Also, make sure your code resets the default values of the fields and gives user the cursor when user clicks on any field.
That's all. I'll give you the php and HTML code [make sure you keep your JS variables consistent with my variable names ($Var1, $myVar1, etc.)]
PS. The maximum amount I'm willing to spend on something simple like this is $30. All other bids are auto-rejected.