Jasper and Crewella Dahvill were married in year 0. They filed joint tax returns in years 1 and 2. In year 3, their relationship was strained and Jasper insisted on filing a separate tax return. In year 4, the couple divorced. Both Jasper and Crewella filed single tax returns in year 4. In year 5, the IRS audited the couples joint year 2 tax return and each spouses separate year 3 tax returns. The IRS determined that the year 2 joint return and Crewellas separate year 3 tax return understated Crewellas self-employment income causing the joint return year 2 tax liability to be understated by $5,100 and Crewellas year 3 separate return tax liability to be understated by $8,900. The IRS also assessed penalties and interest on both of these tax returns. Try as it might, the IRS has not been able to locate Crewella, but they have been able to find Jasper.

a. What amount of tax can the IRS require Jasper to pay for the Dahvills year 2 joint return?

b. What amount of tax can the IRS require Jasper to pay for Crewellas year 3 separate tax return?