A quadratic function is given by g(x)=ax2+b. The function satisfies all of the following conditions:
• The average rate of change of g on [1,3] is 8.
• The instantaneous rate of change of g at x=3 is 12.
• g(3)=20.
What is the value of b?
a) −4
b) 2
c) −2
d) 0