IF Value is Entered, Text is Input

Hey Team! I have taken over a spread sheet at work for my uncle's business expenses, my aunt has done a good job with data entry, a tad old school however. I know there's an easier way verses typing out a word a letting autofill do its thing, so here's my dilemma:

Each category on a Schedule C has a line number and description.
· 8 - Advertising
· 9 - Car & Truck
· 11: Contract Labor
...And so on and so forth.

So what formula would I need to play so that when I type the number 8, it changes the value to Advertising?

Thanks!

Perhaps VLOOKUP

Create a table with (for example) the number in Column X and Description in Column Y

If Line no is C2 and description is in D2

in D2

=VLOOKUP($C2,$X$2:$Y$20,2,FALSE) so your table is in range X2:Y20