\left \{ {{\frac{x+y}{2}=15} \atop {\frac{x-2+\frac{y}{2}}{2}=10}} \right.
\left \{ {{x+y=30} \atop {x-2+\frac{y}{2}=20}} \right.
\left \{ {{x=30-y} \atop {30-y-2+\frac{y}{2}=20}} \right.
\left \{ {{x=30-y} \atop {28-y+\frac{y}{2}=20}} \right.
\left \{ {{x=30-y} \atop {56-2y+y=40}} \right.
\left \{ {{x=30-y} \atop {-y=40-56}} \right.
\left \{ {{x=30-y} \atop {-y=-16}} \right.
\left \{ {{x=30-y} \atop {y=16}} \right.
\left \{ {{x=30-16} \atop {y=16}} \right.
\left \{ {{x=14} \atop {y=16}} \right.