Charles and Joan Thompson file a joint return. In 2014, they had taxable income of $81,240 and paid tax of $12,237. Charles is an advertising executive and Joan is a college professor. During the fall 2015 semester, Joan is planning to take a leave of absence without pay. The Thompsons expect their taxable income to drop to $63,000 in 2015. They expect their 2015 tax liability will be $8,546, which will be the approximate amount of their withholding. Joan anticipates that she will work on academic research during the fall semester. During September, Joan decides to perform consulting services for some local businesses. Charles and Joan had not anticipated this development. Joan is paid a total of $26,000 during October, November, and December for her work. Use the appropriate Tax Rate Schedules. a. What estimated tax payments are Charles and Joan required to make, if any, based on the estimated tax liability for tax year 2015?