Integration by Substitution. The rate of growth of Grass carp, one of the most common type of fish, was modelled by the equation 3x+9 f\"): 2+6x+3 X where t is measured in years and f(t) in kilograms per year. Consider the integral 2 3x+9 2dx o x +6X+3 After substitution into u, the new integral can be written (1 fidu au (a) The value ofA is 09 Ox O3x+3 03x 01.5 Ox+3 00 03 (b) The upper limit of integration b is 03 019 02 038 0-19 O3 00 05