\[\boxed{\text{18.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[x + 120 = 200\]
\[x = 200 - 120\]
\[x = 80.\]
\[x + 20 = 200\]
\[x = 200 - 20\]
\[x = 180.\]
\[x\ больше\ во\ втором\ уравнении,\ \]
\[так\ как\ 180 > 80.\]
\[x = 240\ :5\]
\[x = 48.\]
\[x = 240\ :10\]
\[x = 24.\]
\[x\ больше\ в\ првом\ уравнении,\ \]
\[так\ как\ 48 > 24.\]
\[x = 72\ :9\]
\[x = 8.\]
\[x = 72\ :8\]
\[x = 9.\]
\[x\ больше\ во\ втором\ \]
\[уравнении,\ так\ как\ 9 > 8.\ \]