To find the percent by volume of benzene in the solution, use this formula[tex]\mathsf{Percent\ by\ volume = \left( \dfrac{volume\ of\ solute}{total\ volume\ of\ solution} \right) \times 100}[/tex][tex]\mathsf{= \left( \dfrac{15}{15 + 70} \right) \times 100}[/tex][tex]\mathsf{= \left( \dfrac{15}{85} \right) \times 100}[/tex][tex]\mathsf{= 0.1765 \times 100}[/tex][tex]\mathsf{= 17.65\%}[/tex][tex]\boxed{\mathsf{17.65\%\ benzene\ by\ volume}}[/tex]