I got it. My answer is just close enough. It's 1.40 x 10-2.
This is what I did: I calculate the molar concentration of OH- from the given pH. Then I input it in the ICE table which is
C6H5COO- + H2O --> C6H5COOH + OH-
x - 4.26 x 10-6 +4.26 x 10-6 + 4.26 x 10-6
Then, I calculate x. x squared is the Ksp.