How many days did carol work at the restaurants during the 28 day period ?

[tex]\bf \underset{\frac{1}{4}\textit{ of 28}}{\stackrel{\textit{at the Bookstore}}{\cfrac{1}{4}(28)}}\implies \cfrac{28}{4}\implies 7~\hfill \underset{\frac{1}{14}\textit{ of 28}}{\stackrel{\textit{did not work}}{\cfrac{1}{14}(28)}}\implies \cfrac{28}{14}\implies 2 \\\\\\ \stackrel{\textit{remaining days}}{28 - 7 - 2}\implies 28-9\implies \stackrel{\textit{at the Restaurant}}{19}[/tex]