This year, Paula and Simon (married filing jointly) estimate that their tax liability will be $200,000. Last year, their total tax liability was $170,000. They estimate that their tax withholding from their employers will be $175,000. Required: a. Are Paula and Simon required to increase their withholdings or make estimated tax payments this year to avoid the underpayment penalty? b. By how much, if any, must Paula and Simon increase their withholding and/or estimated tax payments for the year to avoid underpayment penalties