$ \begin{array}{l} a.\left\{ \begin{array}{l} 2x - 3y = 10 \\ - x + 6y = 6 \\ \end{array} \right. \to \left( {8\frac{2}{3},2\frac{4}{9}} \right) \\ b.\left\{ \begin{array}{l} 3x + 5y = 0 \\ 6y - 2x = 12 \\ \end{array} \right. \to \left( { - 2\frac{1}{7},1\frac{2}{7}} \right) \\ c.\left\{ \begin{array}{l} x + y = 1 \\ x + 2y = 100 \\ \end{array} \right. \to \left( { - 98,99} \right) \\ \end{array} $