[tex]\boxed{\begin{array}{l}\begin{cases}\sf c+m=30\\\sf 4c+2m=100\end{cases}\\\underline{\rm multiplicando~a~1^{a}~equac_{\!\!,}\tilde ao~por~-2~temos:}\\+\underline{\begin{cases}\sf-2c-\diagdown\!\!\!\!\!2m=-60\\\sf4c+\diagdown\!\!\!\!\!2m=100\end{cases}}\\\sf2c=40\\\sf c=\dfrac{40}{2}\\\sf c=20\\\sf c+m=30\\\sf 20+m=30\\\sf m=30-20\\\sf m=10\\\sf portanto~h\acute a~20~carros~e~10~motos.\end{array}}[/tex]
