$13.$ In an alkylation process, $10,000$ barrels of butylene are reacted with excess isobutane to produce $20,000$ barrels of high$-$octane gasoline. What is the excess isobutane in barrels?

$14.$ A refinery produces $60,000$ barrels of diesel with a density of $0\mathrm{.}85$ g$/$cm$^3.$ What is the total volume of diesel produced in cubic meters?

$15.$ If a cracking unit processes $40,000$ barrels of heavy oil and yields $25,000$ barrels of gasoline, what is the conversion rate of heavy oil to gasoline?