The Excess Gibbs energy of a binary liquid mixture at $T$ and $P$ is given by:

$\frac{G^E}{RT}=(-2\mathrm{.}6x_1-1\mathrm{.}8x_2)(x_1)(x_2)$

Find the expression: $(\frac{G^B}{RT}{)}_1$ and $(\frac{G^E}{RT}{)}_2$