Keith, a calendar year taxpayer, filed a return correctly showing an income tax liability of $12,000 for 2018. During 2019, his AGI is $110,000 and his income tax liability is $35,000. To avoid a penalty for 2019, Keith must make aggregate estimated tax payments of at least:

a. $35,000.

b. $31,500.

c. $12,000.

d. $10,800.

e. None of the above.