A Credit Shelter Trust generates $35,000 in gross ordinary income (interest and non-qualifying dividends; no capital gains or losses) during calendar year 2018, and incurs $3,000 in Trustee's Fees. The trust distributes $16,000 to the sole beneficiary of the trust, and accumulates the balance of the net income for reinvestment purposes. For Federal Fiduciary Income Tax purposes, what is the highest marginal fiduciary income tax bracket of the trust during calendar year 2018 based on its taxable income?