Answer
$2r^2-7rs+3rt+3s^2-4st+t^2$
Work Step by Step
$(r-3s+t)(2r-s+t)=r(2r-s+t)-3s(2r-s+t)+t(2r-s+t)=2r^2-rs+rt-6rs+3s^2-3st+2rt-st+t^2=2r^2-7rs+3rt+3s^2-4st+t^2$
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