Simple calculator for Drupal site

We want to let the users to calculate an approx. price for house thermo insulation with filling a webform. The fields are: 1. Yout name: (input text box) [login to view URL]: (where to send the calculation) 3. Area to insulate: ...m2 4. Insulation width: ...cm 5. Inside or outside: (radio button - the calculating is different for inside and outside) . Only basic calulating operation needed (+, *)