let's firstly convert the mixed fractions to improper fractions, and then add and subtract.
[tex]\bf \stackrel{mixed}{1\frac{1}{2}}\implies \cfrac{1\cdot 2+1}{2}\implies \stackrel{improper}{\cfrac{3}{2}}~\hfill \stackrel{mixed}{2\frac{1}{4}}\implies \cfrac{2\cdot 4+1}{4}\implies \stackrel{improper}{\cfrac{9}{4}} \\\\\\ \stackrel{mixed}{3\frac{2}{3}}\implies \cfrac{3\cdot 3+2}{3}\implies \stackrel{improper}{\cfrac{11}{3}} \\\\[-0.35em] ~\dotfill[/tex]
[tex]\bf \cfrac{3}{2}+\cfrac{9}{4}-\cfrac{11}{3}\implies \stackrel{\textit{using an LCD of 12}}{\cfrac{(6)3+(3)9-(4)11}{12}}\implies \cfrac{18+27-44}{12}\implies \cfrac{1}{12}[/tex]
