Writing a function in .xla file

Hi.
I want to make a xla file, and i wanted to write a function in that file. The function will pass the input to the sheet in xla file and same sheet will calculate the results the function should read these values and send to the parent workbook. for your referncwe i am attaching a .xls file which will finally be saved as xla file.
In witing a function i am not able to sen input data from function to sheet in xla