Hi Munmun and welcome to the forum!
The forum doesn't provide attachment functionality, so you would have to upload your image to some webspace and give us a link.
However, from what you have described you might want to use code to perform the calculations. You could attach whatever calculations you need to execute to the OnAfterChange event of the dropdown. To do this, find the drop-down node in the Data Source task pane, double-click it, switch to the Data Validation tab, choose OnAfterChange from the event handler drop-down and then click Edit Form Code.
I hope this helps!
Matt Faus / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge