Ten years ago, Liam, who is single, purchased a personal residence for $340,000 and took out a mortgage of $200,000 on the property. In May 2018, when the residence had a fair market value of $440,000 and Liam owed $140,000 on the mortgage, he took out a home equity loan for $220,000. He used the funds to purchase a fully-equipped recreational vehicle, which he uses 100% for personal use.

If the RV was the security for the loan, the maximum amount of debt on which Liam could deduct interest is ?