Afield project superintendent earns an annual salary of $72,800, and she contributes $7900 per year to her 401(k) plan. if she has a required deduction for income taxes (federal, state, and local combined) of 28% of pretax income, how much does she have withheld in income taxes per year?

Contributions to one's 401K plan are taken out without paying tax on them (they are pre-tax contributions). In the end, when you retire you will pay taxes on the money but it is deferred for now.

What this means in terms of the question is that we should deduct the $7,900 first and then take 28% of what is left for taxes.

This person's salary is $72,800 a year and they set aside $7,900 for their retirement account (401K) so that leaves $72800-$7900 = $64,900

She now pays taxes of 28% on this amount ($64,900). Percent means "out of 100" so 28% means and to find 28% of 64900 we multiply (64900)(.28) = $18172.

That is she has $18,172 withheld in taxes each year.