k_a for C6H5COOH = 6.33 x 10-5
First dissolve the salt. Then determine how each ion reacts with water.
C6H5COONa : Na+(aq) + C6H5COO-(aq)
Na+(aq) + H2O : no reaction, ...
The solution explains through line-by-line calculations the steps necessary to find the pH of sodium benzoate as described by the questioner.