Answer: 1
##Explanation: 1.1
  *
  |__"River rhin is considered polluted (total pollution 100)"
  |  |__"company a contributed 30 to chemical pollution"
  |  |__"company b contributed 60 to chemical pollution"
  |  |__"farm c contributed 10 to chemical pollution"
  |  |__"farm c contributed 30 to nutrient pollution"

##Total Explanations:   1