Answer
538.7 gal
Work Step by Step
The size of the tank is
$3ft\times6ft\times4ft=72ft^3$
$72ft^3\times\frac{62.4lb}{1ft^3}\times\frac{1gal}{8.34lb}=\frac{4492.8}{8.34}gal=538.7gal$
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