$\left \{ {{x + y = \frac{4x - 3}{5}} \atop {x + 3y = \frac{15 - 9y}{14}}} \right.$
⇔ $\left \{ {{5x + 5y = 6x - 3} \atop {14x + 42x = 15 - 9y}} \right.$
⇔ $\left \{ {{x + 5y = -3} \atop {14x + 51y = 15}} \right.$
⇔ $\left \{ {{x = 12} \atop {y = -3}} \right.$
