Julie, being self-employed, is required to make estimated payments of her tax liability for the year. Her tax liability for 2017 was $25,000, and her AGI was less than $150,000. For 2018, Julie ultimately determines that her income tax liability is $18,000. During the year, however, she made the following payments, totaling $13,000: April 17, 2018 June 15, 2018 September 17, 2018 January 15, 2019 Total paid $4,500 2,800 4,100 1,600 $13,000 Because Julie prepaid so little of her ultimate income tax liability, she now realizes that she may be subject to the penalty for underpayment of estimated tax a. Determine Julie's exposure to the penalty for underpayment of estimated tax. Based on this information, Julie's required annual payment for estimated taxes should have been , and each quarterly instalment would have been s The amount by which Julie underpaid her estimated tax is s b. If Julie's tax liability for 2017 was $15,960, determine Julie's exposure to the penalty for underpayment of estimated tax. Julie's required annual payment for estimated taxes should have been , and each quarterly installment would have beern .The amount by which Julie underpaid her estimated tax is