Helen and John Wick filed jointly in Year 1. They divorced i…

Helen and John Wick filed jointly in Year 1. They divorced in Year 2. Late in Year 2, the IRS discovered that the Wicks underpaid their Year 1 taxes by $2,000. Both Helen and John worked in Year 1 and received equal income but John had $2,000 less tax withheld than Helen did. Who is legally liable for the tax underpayment?