Can u please elaborate from where this formula comes in solution and how they put it

Q. What is the pH at equivalence point in the titration of 0.1 MCH₃COOH and 0.1 M NaOH?
         (K_a for acetic acid is 1.8 × 10^–5)

     (a) 7

     (b) Between 7 and 8
 
     (c) Between 8 and 9

     (d) Between 6 and 7

$$\begin{gathered} \mathbf{sol}\mathbf{.}\mathbf{\left(}\mathbf{c}\mathbf{\right)}\mathbf{ }\mathbf{ }\mathbf{ }\mathrm{For} \mathrm{weak} \mathrm{acid} \mathrm{and} \mathrm{strong} \mathrm{base}, \\ \mathrm{pH} = 7 +\frac{1}{2}{\mathrm{pK}}_{\mathrm{a}}+\frac{1}{2}\mathrm{logC} \\ = 7 +\frac{4.74}{2}+\frac{1}{2}\log {10}^{-1} \\ = 8.87 \end{gathered}$$