Find y in terms of m and n

$\boxed{x + y = 2m}$

$\boxed{x - y = 2n}$

$\boxed{x + y} + \boxed{x - y} = 2m + 2n$

$2x = 2m + 2n$

$\color{#20A900}\boxed{x = m + n}$

—————————————————————————————————————————————————————————————————

$\boxed{x + y = 2m}$

$m + n + y = 2m$

$y = 2m - m - n$

$\color{#20A900}\boxed{y = m - n}$

Subtract the 2 equations to get y=m-n.