Answer
$$m =0.629 \space kg$$
Work Step by Step
$$0.9867 \space \frac{g}{mL} \times \frac{8.50 \space g_{acetone}}{100 \space g} = 0.0839 \space g_{acetone}/mL$$
$$V = 7.50 \space L \times \frac{1000 \space mL}{1 \space L} = 7500 \space mL$$ $$d = \frac{m}{V} \longrightarrow m = d \times V$$ $$m = 0.0839 \space g/mL \times 7500 \space mL \approx 629 \space g$$ $$m = 629 \space g \times \frac{1 \space kg}{1000 \space g} = 0.629 \space kg$$
