a
(A) \({\text{10}}{\text{.81}} = \frac{{{\text{10}}{\text{.01}}{{\text{x}}_{\text{1}}} + 11.01{x_2}}}{{{x_1} + {x_2}}}\)

\(10.81x_l + 10.81x_2 = 10.01 x_1 + 11.01 x_2\)

\(10.81 x_1  - 10.01 x_1 = 11.01 x_2 - 10.81 x_2\)

\(0.80\, x_1 = 0.20\, x_2\)

\(\frac{{{x_1}}}{{{x_2}}} = \frac{{20}}{{80}}\,,\,\,\,\,\,{x_1} = 20\,,\,\,\,\,\,\,{x_2} = 80\)