Answer
$$d = 0.792 \space g/mL$$
Work Step by Step
$$m_{acetone} = 437.5 \space lb - 75.0 \space lb = 362.5 \space lb$$ $$m_{acetone} = 362.5 \space lb \times \frac{1 \space kg }{2.20 \space lb} \times \frac{1000 \space g}{1 \space kg} \approx 164800 \space g$$ $$V = 55.0 \space gal \times \frac{1 \space L}{0.264 \space gal} \times \frac{1000 \space mL}{1 \space L} \approx 208000 \space mL$$
$$d = \frac{m}{V} = \frac{164800 \space g}{208000 \space mL} = 0.792 \space g/mL$$
