According to the BP 2010 Statistical Review of World Energy the fol- lowing figures applied at the end of 2009: . Proved natural gas reserves at the end of 2009: 187.49 trillion cubic meters . Natural gas production 2009: 2986.96 billion cubic meters (a) What is the WRLI for natural gas 2009 at 2009 production levels? (b) What would be the value for the WRLI for natural gas if we assumed that gas production would rise annually by 3% until depletion was complete? (c) What would be the value for the WRLI for natural gas if we assumed that gas production would fall annually by 3% until depletion was complete? (d) Plot the corresponding depletion curves for natural gas, assuming: linear depletion of natural gas based on 2009 production levels. ii progressive depletion with production levels for natural gas rising annually by 3%. (iii) declining depletion with production levels for natural gas falling annually by 3%