Alright so:

c = n/V

For the sodium acetate

0,025moles/L = 0,005moles/V

V = 0,2 L = 200 mL

For acetic acid I calculated:

c =n/V

0,1moles/L = n/0,15L

0,015 moles = n

And then I calculated the new concentration of sodium acetate and acetic acid considering the new volume of 350 mL (100mL + 250mL)

The concentration for the acid is: 0,0428 moles/L and for the salt: 0,0142 moles/L

I put this in the Henderson-Hasselbach equation, which gave me a pH of around 4, which is consistent with what is requiered.

I am sensing a major mistake here, what did I do wrong?

Thanks!!