[tex]12 \frac{1}{4} = \frac{12*4+1}{4} = \frac{48+1}{4} = \frac{49}{4} = \frac{147}{12} \\ \\ 7 \frac{2}{3} = \frac{7*3+2}{3}= \frac{21+2}{3}= \frac{23}{3} = \frac{92}{12}\\
\\3= \frac{36}{12}\\
\\ 7\frac{2}{3}+3= \frac{92}{12}+ \frac{36}{12} = \frac{92+36}{12} = \frac{128}{12} \\ \\
12 \frac{1}{4}-7 \frac{2}{3}-3= \frac{147}{12}- \frac{128}{12}= \frac{147-128}{12}= \frac{19}{12}[/tex]