Simple calculator with predefined coeficient I would like to have very simple calculator on my page - user should input any number x (days) and the result should be x times y where y is any preddefined coeficient that I define. 
Is it possible to do in drupal. 6 or 7 version?
Thank you
Yes - this is possible, but its not really related to Drupal (at least the way you define it). Its either going to be a javascript calculator that you embed in a page (where the result wouldn't get saved) or a PHP function that processes the results from a form and returns the result on the next page. 

Either way, both are beyond the scope of this site but tutorials like this one should give you a start on writing your calculator embed.