Как решить это уравнение?

Решите задачу:

$\left \{ {{ \frac{x+y}{8}+ \frac{x-y}{6}=5 } \atop {\frac{x+y}{4}+\frac{x-y}{5}}=10} \right. \\ \left \{ {{\frac{x+y}{4}+ \frac{x-y}{3}=10} \atop {\frac{x+y}{4}+\frac{x-y}{5}}=10}} \right. \\ \left \{ {{\frac{x-y}{3} - \frac{x-y}{5} =0} \atop {\frac{x+y}{4}+\frac{x-y}{5}}=10}} \right. \\ \\ \left \{ {{x-y=0} \atop {x+y=40}} \right. =\ \textgreater \ x=y=20 \\$