App for Severance Payment Calculation

In essence, the app calculates the corresponding severance payment for an employee who is terminated from employment. The total is based on a formula which takes into consideration the total amount of years worked and the highest annual/monthly salary the employee has obtained. Accordingly, the app needs a box to enter the date of hire, a box to enter the date of termination, and a box to enter the highest annual/monthly salary, and a box which gives the total. I would like the app to look like a clean sheet of a legal pad and when the amounts are entered to look as if they were being written in pencil, with the corresponding box dissapearing. The app would need to include some legal disclaimers, and some explanations for each corresponding box. I would also provide the applicable formula, which is very simple and straightforward. Thanks a lot,