Mark owns his home and has a $250,000 mortgage related to his purchase of the residence. When his daughter went to college in the fall of 2018, he borrowed $20,000 through a home equity loan on his house to help pay for her education. The interest expense on the main mortgage is $15,000, and the interest expense on the home equity loan is $1,500. How much of the interest is deductible as an itemized deduction and why?