User Input form into formula

I am putting together a modelling spreadsheet that will show the cost of items we currently buy if they go up by a certain percentage. Since this is sensitive I have made a very basic model of it. I have a couple of questions:

1) How can I take the user's input from the UserForm1 and put it into the formula =(B5+(B5/100)*2) (The red two is percentage of increase that I would like the user to be able to input via the form)
2) How can I get this to apply to all of the items in the list?
3) Is it possible it possible to be able to revert back to the original figures as this is only for modelling purposes?