\(\begin{aligned} \text{I} & & 5x-6y & =-64 & & |\,\cdot3\\ \text{II} & & 6x+9y & =69 & & |\,\cdot2\\ \\ \text{III} & & 15x-18y & =-192\\ \text{IV} & & 12x+18y & =138\\ \\ \text{III+IV} & & 27x & =-54 & & |\,:27\\ & & x & =-2\\ \\ \text{in I einsetzen} & & 5\cdot\left(-2\right)-6y & =-64 & & |\,+10\\ & & -6y & =-54 & & |\,:\left(-6\right)\\ & & y & =9 \end{aligned}\)
