How to replace a cell with a formula?

What I want to do is create a macro and make that macro a button for anyone who opens this page avaiable for use. Let me describe as below. I have an inventory sheet and want to update.
Column B is current inventory level
Column C is for incoming inventory
Column D is for items taken from inventory
Column E is the new inventory quantity

What I want is to have the macro do the math to come up with a new inventory quantity in E, then have that quantity replace what is in B and then delete all items in C,D and E, while leaving the new inventory quantity in B. I know I can just sum to come up with a number in E, but how can I make it replace what is in B and then delete everything, getting it ready for the next entry? If I am too vague, please ask for further details. Thanks so much for any help in advance.

Let me try either of those and let you know. Thanks for the help. I'm sorry for the confusion. Maybe I'm making more of this than needs to be made.