Ms. Lee, a single adult, earned $65,000 in taxable income last year. Use the rate table below to calculate how much she must pay in income taxes? 2013 U.S. Federal Income Tax Rates for Single Adults 10% on taxable income from $0 to $8,925, plus 15% on taxable income over $8,925 to $36,250, plus 25% on taxable income over $36,250 to $87,850, plus 28% on taxable income over $87,850 to $183,250, plus 33% on taxable income over $183,250 to $398,350, plus 35% on taxable income over $398,350 to $400,000, plus 39.6% on taxable income over $400,000.

Ok so we know that she pays a 10% tax for her first $8925, so she will pay $892.50
She will pay an extra 15% of income from $8925 to $36250, so she will pay 15% of 27325 (36250-8925), which is $4098.75
Then she pays 25% of income from $36250 to $87850, but she only earns $65000, so she will pay 25% of $(65000-36250), or 25% of 28750 which is $7187.50.

So in total she will pay $892.50 + $4098.75 + $7187.50
And that amount is $12178.75
So Ms. Lee needs to pay $12178.75 in tax

Hope this helped