Hiding constant values in formulas

agristwood 

There are multiple ways to accomplish that. And you are to be commended for asking the question. One of the ground rules of good formulas is to avoid "hard-coding" variables (even if "constant") into formulas; even constants change from time to time.  I notice in your image that you're only asking about the second 8; as such, it's not clear if they're really the same--i.e., if one changes so does the other--or not. I'll just address your question, but the advice to avoid hard-coding of variables applies really to both.

The simplest way is to have a single cell reference, placing it off to the side (maybe even on another sheet) and make it absolute rather than relative (also important terms to learn).

=((D4-C4)*8)+$K$2

Another is via a "named range" -- this latter has the advantage of making the formula easier to read.

=((D8-C8)*8)+BaseHrs

See the attached spreadsheet. And feel free to come back with questions. (Note too, those are hyperlinks above in blue, links to a helpful website that explains both concepts)

Then there are ways, in cases where that variable changes based on multiple factors (length of service, age, whatever) and then a table with lookup functions can come into play. We'll leave that for a later time.