Custom Carbon Dioxide/Pollution calculator

Hello,

I would like to place a calculator/form on my WordPress website of the bicycle courier company. (http://www.bikekoeriertilburg.nl)(Dutch)

First it should be a calculator/form where the potential costumers can fill in the amount of driven kilometres (in a chosen car).

Second it is preferable if the customer can choose in a drop down menu between ‘car’/’van’/’truck’. This because the difference in pollution/carbon dioxide admission.
If to difficult, it is possible to skip this and just take an average of all vehicles.

Third it is preferable if the customer in a drop down menu can select between ‘every day’ / ‘every week’ / ‘every month’.

As a result of that the calculator/form should give the ‘amount of trees/m3 of forest’ needed to compensate the carbon dioxide in a year time for that specific ride.

By a company in The Netherlands I already got the ‘rough-and-ready rule’ about the conversion of this all, so I can already calculate this by hand.

The above calculator should give potential costumers more information/reasons why to choose for the bicycle courier.

What is the easiest way to create something like this on my website?!
Preferably a plug-in, but otherwise an other way to achieve something like this.

All tips & tricks are very welcome,

Bas