$3.$ A hydrocracking unit processes $50,000$ barrels of heavy oil per day with an average sulfur content of $2\%.$ If the unit removes $90\%$ of the sulfur during processing, how many kilograms of sulfur are removed daily?

$4.$ If a reforming unit upgrades $20,000$ barrels of naphtha with an octane number of $80$ to high$-$octane gasoline with an octane number of $95,$ what is the total volume of high$-$octane gasoline produced, assuming a density of $0\mathrm{.}75$ g$/$cm$?$