Answer
3
Work Step by Step
Since the coefficient of the squared term is one, we know that the expression must factor to:
$$ (b\pm a)(b\pm k)$$
Here, we see that a and k must multiply to get $9$ and add to get $-6$. Thus, we find that the solution is:
$$(b-3)^2$$
Thus, setting each factor equal to zero, we find that the solutions are:
$$3$$