Henderson Hasselbach question:

Consider a simple pH indicator dye that changes color with pH$.$ Let's suppose that our dye absorbs strongly at a given wavelength at pH $12$ while it has essentially no absorbance at pH $2$ as shown in the table below

dye concentration pH Abs

$10$ micromolar $20\mathrm{.}00$

$10$ micromolar $120\mathrm{.}90$

At pH $7$ you observe the absorbance of your $10$ micromolar solution to be $0\mathrm{.}3$

Calculate the pKa to $2$ significant figures

You can assume that our dye is a simple monoprotic acid that is fully deprotonated at pH $12$ and fully protonated at pH $2.$