If I owe IRS for 2020 and I am mailing my 2020 1040 now. How much should the check say? Interest and Penalties Question.

So I just did my 2020 federal taxes with turbotax desktop and I owe the IRS $21.00.

 

A) Mail them a check for $21.00

B) Can the interest & penalties be figured out now? Then mail them a check for the $21.00 + Interest + Penalties.

C) ?