For a particular taxable year, X Corp., a DE corp., has taxable income of $$1,000($before taking foreign income taxes into account$),$ of which $$200$ is from sources outside the U$.$S$.$ Assume the U$.$S$.$ corporate tax rates is $21\%,$ and that the foreign tax credit is limited to the U$.$S$.$ tax on foreign$-$source income. What is Xs U$.$S$.$ tax liability for the year if$,$ alternatively, it incurs foreign income taxes for the year of:

a$.$ $$20?$

b$.$ $$75?$