You are looking for the difference between interest paid for a 15 year mortgage or 25 year mortgage. Since some interest will be paid for both, this is why the answer is D--it is the difference between them.
6) Irene Farley earns a semimonthly salary of $7714.27. She has a $100 adjustment-to-income flexible benefits package, is married, and claims 4 withholding allowances. Find the federal tax withholding to be deducted from her semimonthly paycheck using the percentage method tables.