I am trying to do some calculations in a table on forms 10.4. I am new to using any calculations within forms, and the ones i have found and tried are not working or giving an error.

The first calculation I am trying to do is calculating time entered. This form will use military time, and i need it to calculate total hours worked based on clock in time and clock out time. 

The next calculation I am wanting to do is to calculate total mileage used. based on Starting and ending Mileage. 

Does anyone have a simple calculation I can use in these instances. Thank you in advanced for your help.