The cost (in dollars) of producing x units of a certain commodity is C(x)=3500+10x+.4x^2 (a) Find the average rate of change of C with respect to x when the production level is changed (I) from x= 100 to x= 105 (II) from x=100 to x=101 (b) Find the instantaneous rate of change of C with respect to x when x=100