Okay I need help on figuring out 1.C.and 1.D.

I have calculated 1.A. and 1.B. with the above documentation but need help on the last two questions.

Thank you

Monthly Mortgage PMT = $2,046.47

Principal Value after 3 Years = $414,274.49

c). What is the total interest paid for this 30-year mortgage loan?

d).What is the loss of tax shield if Dustin opts for 15-year mortgage with APR of 3.8% and the tax rate is 35%?