On mixing, heptane and octane form an ideal solution. At $373\text{ K}$, the vapour pressures of the two liquid components (heptane and octane) are $105\mathrm{kPa}$ and $45\mathrm{kPa}$

respectively. Vapour pressure of the solution obtained by mixing $25\mathrm{g}$ of heptane and $35$g of octane will be (molar mass of heptane $=100\mathrm{g}{\mathrm{mol}}^{-1}$ and of octane

$\left.=114\mathrm{g}{\mathrm{mol}}^{-1}\right)$