Removing #DIV/0!

I have a long row of 18 cells showing me DIV/0. Their values are dependant upon data in another workbook. I only need to enter the values in 6 of the 18 cells, which update the DIV/0 leaving me with 12 I don't need. I want to be able to total the 6 values in that row WITHOUT having to delete the other 12 cell formula's. My question is 2 fold. [1]how do i do this [2] when a formula is placed in a cell I can see values in there (00:00.00) awaiting data input. How do I make it so these values cannot be seen.

It's really hard for me to explain this and so I'm hoping the attached will make it clearer to those who are able to help me. And thank you for this.