How many times is silver benzoate more soluble in a buffer solution of hydronium ion concentration $6.46\times {10}^{-4}$ compared to its solubility in pure water? (Report the value after rounding off to integer).

Given: The ionization constant of benzoic acid is $6.46\times {10}^{-5}. K_{sp}$ for silver benzoate is $2.5\times {10}^{-13}.$