The$$ Lees, a family of two adults and two dependent children under age$16,$ had a gross annual income of $$$$74,000\mathrm{.}00$ for $2020.$ Determine their standard deduction and child tax credit$$ amounts, as well as their marginal and average tax$$ rates, assuming their filing status is married filing jointly. Why is their average tax rate lower than their marginal$$ rate?