\[30 < a < 50\]
\[60 < 2a < 100\ \]
\[10 < b < 40\]
\[\ 20 < 2b < 80\]
\[80 < 2a + 2b < 180\ \ \ \ \ \ \ \ \ \ \ \]
\[300 < ab < 2000\]
\[То\ есть:\ \]
\[80 < P < 180\]
\[300 < S < 2000.\]