asking for help

the segment from (1,3) to (-2,1) is extended twice its own length

find the terminal point

$\begin{array}{|rcll|} \hline &&\displaystyle 3 \cdot \left[ \binom{-2}{1} - \binom{1}{3} \right] + \binom{1}{3} \\\\ &=& \displaystyle 3 \cdot \binom{-2-1}{1-3} + \binom{1}{3} \\\\ &=& \displaystyle 3 \cdot \binom{-3}{-2} + \binom{1}{3} \\\\ &=&\displaystyle \binom{-9}{-6} + \binom{1}{3} \\\\ &=&\displaystyle \binom{-9+1}{-6+3} \\\\ &=& \displaystyle \binom{-8}{-3} \\\\ \hline \end{array}$