What is the [C7H5O2−] in a solution which is 0.1283 M in HC7H5O2 and 0.1364 M in HBr?

HC7H5O2(aq) + H2O(l) « C7H5O2−(aq) + H3O+(aq)
Ka = 6.5000e-5

Those formula don't mean anything to me. If you write them in acid/base notation, which I suspect they are, it would be easier. At any rate, look at your post above and see if it isn't worked the same way.