Aaron and Hazel, married taxpayers, took out a mortgage on their home for $350,000 in 2002. In May of 2008, when the home had a fair market value of $375,000 and they owed $300,000 on the mortgage, they took out a home equity loan for $220,000. They used the funds to purchase a single engine airplane to be used for recreational travel purposes. What is the maximum amount of debt on which they can deduct home equity interest?