9 Question 1 of 35. To avoid a penalty for underpayment of estimated tax for 2021, a sole proprietor with an Al below 5150,000 (375,000 WES) should make estimated payments in the amount of the smaller of of the tax shown on their 2020 return or of the tax shown on their 2021 return 50%, 90% 90%, 50% 90% 100% 100%; 90% 3 Enter Mark for follow up