A 1.00 L buffer solution is 0.250 mol L-1 in HF and 0.150 mol L-1 in NaF. Calculate the percent change in pH of the solution after the addition of 50.0 mL of 1.00 mol L-1 HCl. The Ka for HF is 3.5x10-4. Report your answer in 2 significant figures.