You should have

Remember, we can't see your database - you didn't mention the field name of
which we need to find 10% . I'll call it JobAmount. JobAmount may be a field
in a Totals query if you are adding up everything you need for your job.

I recommend that you have a field in your Jobs table called DeposPerc where
you store the 10 (I'd make it a number field rather than a percent - it's
easier to manage.). Don't put it in your calculation because if you decide
to change your deposit percentage it will make your past records wrong.

The calculation in your query is
Deposit: JobAmount * ([DeposPerc]/100)
Don't store the results of  calculations in your table however, just in your
query. Here, it will be available for display in forms and reports. If you
store it in your table and then change one of the values that add up to
JobAmount, your data in your table will be wrong
Evi

Treat your table as a bucket where you store your data.