Calculating Time in Userform Textbox and Filtering Comboboxes Coding Help

Hello, somehow I need to get my Start / Finish textboxes to total in my Hours textbox, then I do need it to show a total hours for the day. Also, I need to filter my Account Description combobox based on my Account Code combobox. I have attached the file so that you can understand my question better, any help is much appreciated! Thanks