Question

Please help, need answer fast!

Answer 1

Instead of plugging in $m=-2$ and $n=4$ right away, notice that

$m^2-2mn+n^2=(m-n)^2$

and now evaluating this expression at the two given values is easier, if only a little:

$((-2)-4)^2=(-6)^2=(-1)^2\times6^2=1\times36=36$