Annual coal production in the US (in billion tons per year) is given in Table 1. Table 1 Year 1997 1999 2001 2003 2005 2007 2009 Rate 1.090 1.094 1.121 1.072 1.132 1.147 1.073 Estimate the total amount of coal produced in the US between 1997 and 2009 by evaluation of the (a) Right-hand sum (b) Left-hand sum