[evrtt103]

How do I calculate the [H30+] if I have 255 ml of a 2.95 M weak acid that is added to 144 mL of a 1.20M of its conjugate base.  I also know the pKb of the base is 3.80. I don't know how to do this without know what acid and base I have to create a balanced equation.

[AWK]

You do not need to create any reaction. Instead, you should do dilution of both solutions and use the Henderson-Hasselbach equation.