401K and Income Taxes

The Scenario
"Your friend, Sydney, wants to start contributing to her employer's 401(k) plan to save money for retirement. She wonders how much she would save on her income taxes by contributing to the plan. She can invest up to 7% of her income into the plan. Her current income is US$45,000 per year, and she is in the 15% tax bracket" (CTU online, 2006).

Calculation
In order to calculate how much Sydney owes in taxes I took her total income and subtracted fifteen percent which left her owing a total of $6,750.00. If Sydney invests 1% of her total income, she will be investing $450 and will save $67.50 in taxes. If Sydney invests 2% of her total income, she will be investing $900 and will save $135 in taxes. If Sydney invests 3% of her total income, she will be investing $1,350 and will save $202.50 in taxes. If Sydney invests 4% of her total income, she will be investing $1,800 and will save $270 in taxes. If Sydney invests 5% of her total income, she will be investing $2,250 and will save $337.50 in taxes. If Sydney invests 6% of her total income, she will be investing $2,700 and will save $405 in taxes. If Sydney invests 7% of her total income, she will be investing $3,150 and will save $472.50 in taxes. As you can see, Sydney will save more money if she contributes to her 401K than if she doesn't.