well, is just a matter of addition, namely 4 1/2 + 6 2/3 + 9 1/4.
now, let's change all mixed fractions firstly, to "improper" fractions, and proceed from there,
[tex]\bf \stackrel{mixed}{4\frac{1}{2}}\implies \cfrac{4\cdot 2+}{1}\implies \stackrel{improper}{\cfrac{9}{2}}
\\\\\\
\stackrel{mixed}{6\frac{2}{3}}\implies \cfrac{6\cdot 3+2}{3}\implies \stackrel{improper}{\cfrac{20}{3}}
\\\\\\
\stackrel{mixed}{9\frac{1}{4}}\implies \cfrac{9\cdot 4+1}{}\implies \stackrel{improper}{\cfrac{37}{4}}\\\\
-------------------------------\\\\[/tex]
[tex]\bf \cfrac{9}{2}+\cfrac{20}{3}+\cfrac{37}{4}\impliedby \textit{our LCD is clearly \underline{12}}\implies \cfrac{(6)9+(4)20+(3)37}{12}
\\\\\\
\cfrac{245}{12}\implies 20\frac{5}{12}[/tex]
