\(\left\{{}\begin{matrix}x+y=\dfrac{150}{2}\\x+5=2y-10\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}x+y=\dfrac{150}{2}\\x-2y=-15\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}\left(x+y\right)-\left(x-2y\right)=\dfrac{150}{2}-\left(-15\right)\\x=2y-15\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}3y=90\\x=2y-15\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}y=30\\x=45\end{matrix}\right.\)
\(\left\{{}\begin{matrix}x+y=150\\2\left(x+5\right)=2y-10\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}x+y=150\\2x-2y=-20\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}x+y=150\\x-y=-10\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}2x=140\\y=x+10\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}x=70\\y=80\end{matrix}\right.\)
#$\mathtt{Toru}$
