In an exactly.200m solution of benzoic acid, a monoprotic acid, the [h+] = 3.55 × 10–3m. what is the ka for benzoic acid?

The concentration of benzoic acid is 0.2 M
Using the ICE Method
HC7H6O2 <=> H+          +     C7H6O2-
0.2
-3.55 x 10-3     3.55 x 10-3   3.55 x 10-3                                  

0.189               3.55 x 10-3     3.55 x 10-3
Ka = (3.55 x 10-3)(3.55 x 10-3)/(0.189)
Ka = 6.67 x 10-5