Chapter 17.1, Problem 2CP

What is the pH of a solution prepared by adding $\text{0}\text{.05 mole of NaF to 1}\text{.0 L of 0}\text{.1 }M\text{ HF at 25°C?}$ (Assume that the addition of $\text{NaF}$ does not change the volume of the solution.) $\text{(}{K}_{\text{3}}\text{ for HF =7}\text{.1 }\times \text{ 1}{\text{0}}^{\text{-4}}\text{.)}$

$\begin{array}{l}\text{a})\\ 2.1\\ \text{b)}\\ 2.8\\ \text{c)}\\ 1.4\\ \text{d})\\ 4.6\\ \text{e)}\\ \text{7}\text{.3}\end{array}$