I need help for Windows Workflow Foundation assignment:

Make a Windows application that will perform the calculation of service. The form will enter the start and end dates for the calculation of service. As the length of service can be calculated in three different ways to form there will be a combobox from which to choose which method of calculation we want. Clicking the button will run the calculation obračunaj. For each method of calculation of service there will be a custom activity that will be dynamically loaded in the workflow, depending on the selected item in combobox in. The first method of calculation is that for each month that includes a 31 day, another way means that each month has 30 days, and the third way will be taken for each month of the exact number of days and shall take into account whether it is a leap year.