Решите систему линейных уравнений с двумя переменными. Заранее спасибо.

Решите задачу:

$\left \{ {{0,3x-0,7y=2,4} \atop {1,2y-0,9x=2,7}} \right. \\ \\ \left \{ {{3x-7y=24} \atop {12y-9x=27}} \right. \\ \\ \left \{ {{x= \frac{7y}{3}+8 } \atop {12y-9( \frac{7y}{3}+8)=27 }} \right. \\ \\ \left \{ {{x= \frac{7y}{3}+8} \atop {12y-21y=27+72}} \right. \\ \\ \left \{ {{x= \frac{7y}{3}+8} \atop {y=-11}} \right. \\ \\ \left \{ {{x= -\frac{77}{3}+8 } \atop {y=-11}} \right. \\ \\ \left \{ {{x=-17 \frac{2}{3} } \atop {y=-11}} \right.$

$\left \{ {{2,4x-0,9y=-3,6} \atop {1,2y+0,8x=1,8}} \right. \\ \\ \left \{ {{24x-9y=-36} \atop {12y+8x=18}} \right. \\ \\ \left \{ {{24x+36=9y} \atop {12y+8x=18}} \right. \\ \\ \left \{ {{ y= \frac{8x}{3}+4 } \atop {12*( \frac{8x}{3}+4)+8x=18 }} \right. \\ \\ \left \{ {{y= \frac{8x}{3}+4} \atop {40x=-30} \right. \\ \\ \left \{ {{y= \frac{8(-0,75)}{3}+4} \atop {x=-0,75}} \right. \\ \\ \left \{ {{y=2} \atop {x=-0,75}} \right.$