a
\(P_{\text {Total}}=P_{A}^{\circ} x_{A}+P_{B}^{\circ} x_{B}\)

\( = \,P_{Heptane}^o\) \(x_{\text {heptane}}+P_{Oc\tan e}^o\) \(x_{O c \tan e}\)

\(=105 \times \frac{25 / 100}{\frac{2}{100}+\frac{33}{114}}+45 \times \frac{35 / 114}{\frac{25}{100}+\frac{55}{114}}\)

\(=105 \times \frac{0.25}{0.25+0.3}+45 \times \frac{0.3}{0.25+0.3}\)

\(=\frac{105 \times 0.25}{0.55}+\frac{45 \times 0.3}{0.55}\)

\(=\frac{26.25+13.5}{0.55}=72\, k P a\)