$1\mathrm{.}5$ Which emits more $S{O}_x$ per unit amount of electricity produced: a coal$-$fired plant with a $90\%$ efficient $S{O}_2$ scrubber or an oil$-$fired plant with no scrubber? Assume the coal has a heat content of $13,000B\frac{t}{l}b$ and contains $3\mathrm{.}5\%$ sulfur, and that the oil has a heat content of $6\mathrm{.}0(10{)}^{6}Bt\frac{u}{?}$ barrel $(42$ gallons$)$ and contains $0\mathrm{.}9\%$ sulfur. Assume the oil has a specific gravity of $0\mathrm{.}92.$