Correctly close Excel from within a userform code. Is there a way?

I'm running a small example (attached) of using userforms to collect data and perform some calculations, and worksheets to display the results. After exiting from application an instance of Excel still running as a background process, and needs ending from the Task Manager. I understand that trying to close Excel from within a userform is controversial but I can't figure out how to otherwise do it. Any help, please?