On December $22,2017,$ President Donald Trump signed the Tax Cuts and Jobs Act of $2017($TCJA$)$ into law. The TCJA went into effect on January $1,2018-$ thereby changing the marginal tax rates on income earned during the $2018$ calendar year.

a$)$ Before the TCJA, the marginal tax rates on the income earned by a single filer in $2017$ were:

$\backslash$table$[[$Income tax bracket,$\backslash$table$[[$Marginal$],[$Tax rate$]]],[$$$0$ to $$9,325,10\%$