[tex]\left\{\begin{array}{ccc}x-4y=27\\3x+y=24&|multiply\ both\ sides\ by\ 4\end{array}\right\\\\\underline{+\left\{\begin{array}{ccc}x-4y=27\\12x+4y=96\end{array}\right}\\.\ \ \ 13x=123\ \ \ |divide\ both\ sides\ by\ 13\\.\ \ \ \ \ x=\dfrac{123}{13}\\\\subtitute\ to\ 3x+y=24\\\\3\cdot\dfrac{123}{13}+y=24\\\\\dfrac{369}{13}+y=\dfrac{24\cdot13}{13}\ \ \ \ |subtract\ \dfrac{369}{13}\ from\ both\ sides\\\\y=\dfrac{312}{13}-\dfrac{369}{13}\\\\y=-\dfrac{57}{13}[/tex]
[tex]\left\{\begin{array}{ccc}x=\dfrac{123}{13}\\\\y=-\dfrac{57}{13}\end{array}\right[/tex]
