we'll first off, convert the mixed fractions to "improper", and them add them up like we would any other fractions, by using the LCD.
[tex]\bf \stackrel{mixed}{8\frac{9}{12}}\implies \cfrac{8\cdot 12+9}{12}\implies \stackrel{improper}{\cfrac{105}{12}}
\\\\\\
\stackrel{mixed}{5\frac{5}{12}}\implies \cfrac{5\cdot 12+5}{12}\implies \stackrel{improper}{\cfrac{65}{12}}\\\\
-------------------------------\\\\
\cfrac{105}{12}+\cfrac{65}{12}\impliedby \textit{clearly the}\stackrel{LCD}{12}\implies \cfrac{105+65}{12}\implies \cfrac{170}{12}
\\\\\\
\stackrel{simplified}{\cfrac{85}{6}}\implies 14\frac{1}{6}[/tex]
