how to make program code for application that can calculate postage of goods with android app : [See image][1]
i learning make a application, the application have function to calculate postage of goods from a airport of origin to airport destination
the process description is as follows:
1. choose a airport origin
2. then,choose airport of destination
3. fill actual weight
4. choose a commodity from spinner
5. choose a airline
6. klik CALCULATE button to get postage
7. Postage will be show below of CALCULATE button

What technique will i use to get the postage, is it using SWITCH CASE or IF ?, please give me a reference. I am very happy for your help


  [1]: https://i.stack.imgur.com/xuB7F.png