Решите систему уравнений, пожалуйста {x+y=42 2/3=1/2y

Решите задачу:

$\left \{ {{x+y=42} \atop { \frac{1}{2} y= \frac{2}{3} }} \right. \left \{ {{y=42-x} \atop { \frac{1}{2} *(42-x)= \frac{2}{3} }} \right. \left \{ {{y=42-x} \atop {21- \frac{1}{2} x= \frac{2}{3} }} \right.$
$\left \{ {{y=42-x} \atop { \frac{1}{2} x=21- \frac{2}{3} }} \right. \left \{ {{y=42-x} \atop { \frac{1}{2} x=20 \frac{1}{3} }} \right. \left \{ {{y=42-x} \atop {x=20 \frac{1}{3} : \frac{1}{2} }} \right.$
$\left \{ {{y=42-x} \atop {x= \frac{61}{3} *2}} \right. \left \{ {{y=42-x} \atop {x= \frac{122}{3} }} \right. \left \{ {{y=42-x} \atop {x=40 \frac{2}{3} }} \right.$
$\left \{ {{y=42-40 \frac{2}{3} } \atop {x=40 \frac{2}{3} }} \right. \left \{ {{y=1 \frac{1}{3} } \atop {x=40 \frac{2}{3} }} \right.$