[tex]\bf 4\frac{1}{4}\implies \cfrac{4\cdot 4+1}{4}\implies \cfrac{9}{4}
\\\\\\
3\frac{3}{5}\implies \cfrac{3\cdot 5+3}{5}\implies \cfrac{18}{5}\\\\
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\cfrac{9}{4}+\cfrac{18}{5}\impliedby \textit{we'll use the LCD of 20}\implies \cfrac{(5\cdot 9)~+~(4\cdot 18)}{20}
\\\\\\
\cfrac{45+72}{20}\implies \cfrac{117}{20}\implies 5\frac{17}{20}[/tex]
