[tex]\left\{\begin{array}{ccc}4x+13y=40\\4x+3y=-40&/\cdot(-1)\end{array}\right\\+\left\{\begin{array}{ccc}4x+13y=40\\-4x-3y=40\end{array}\right\\-----------\\.\ \ \ \ \ \ 10y=80\ \ \ \ /:10\\.\ \ \ \ \ \ y=8\\\\4x+3\cdot8=-40\\4x+24=-40\\4x=-40-24\\4x=-64\ \ \ \ /:4\\x=-16\\\\Solution:x=-16\ and\ y=8.[/tex]
