$2.$ T$,$ who is single, a child of X and a full$-$time law student has gross investment income of $$4,000$ in the current year and no $62$ or itemized deductions. For simplicity assume that there are no inflation adjustments. See $ $63($c$)(4),(7)($B$).$ T qualifies as a dependent of X for the year.

a$.$ What is T$\text{'}$s taxable income, if any, for the current year?

b$.$ What difference in result in $($a$),$ above, if instead T has $$1,000$ of earned income and $$3,000$ of investment income?