Find the positive numbers $b$ such that the average value of $f(x)= 2 + 6x - 3x^2$ on the interval $[0, b]$ is equal to 3. List these numbers in increasing order. If any blanks are unused, type an upper-case "N" in them.

Smallest value of $b =$

Next smallest value of $b =$

Next smallest value of $b =$