Estimate the instantaneous rate of change of the national debt at 2006 by using the table bellow and the forward difference quotient that is D(2006 + t) t for t > 0, take for instance t = 1 and backward difference quotient that is D(2006 + t) t for t < 0, take for instance t = 1. Year Debt ($ Billion) 2005 5413 2006 8507 2007 9008