Chapter 9 exercises: graphs

1. 27. x+y LT* 30
   a java compatible browser is needed for this
   
2. 28. 4x+9y LT* 72
   a java compatible browser is needed for this
   
3. 29. 10x+5y LT* 120
   a java compatible browser is needed for this
   
4. 30. 2x+3y GT* 12
   a java compatible browser is needed for this