I am stumped

I basically need to create an input box that prompts the user to enter cash amounts that will be totaled. When the user is finished, they type done or click cancel. I also need to use a Loop Until loop to do this. I've tried everything under the sun - Cdec etc. Nothing works. I'm going to be asking the teacher for some more help but I thought I'd ask here as well.

Every time I run it I get an error that there is a cast mismatch or something..

Anyways, any help would be appreciated.

Thank you