Volume contraction during complete combustion of 39 ml of toluene as per reaction 

${\mathrm{C}}_7{\mathrm{H}}_8+9{\mathrm{O}}_2\to 7{\mathrm{CO}}_2+4{\mathrm{H}}_2\mathrm{O}$

$\text{ 1 mol Toulele }=22400\mathrm{mp}$

$\text{30 mol Toulele }=\frac{30}{22400 \mathrm{mp}} \mathrm{mole}$

$=1.339\times {10}^{-3} \mathrm{mole}$

$\begin{array}{r}1.339\times {10}^{-3}\times 10 \mathrm{mol}\text{ form }\\ \end{array}$

$\frac{1.329\times {10}^{-3}}{10}\times 7 =90 \mathrm{mL}$