Check the picture below.
[tex]\stackrel{X}{1\frac{1}{2}}~~ + ~~\stackrel{X}{1\frac{3}{4}}~~ + ~~\stackrel{X}{1\frac{3}{4}} \\\\[-0.35em] ~\dotfill[/tex]
[tex]\stackrel{mixed}{1\frac{1}{2}}\implies \cfrac{1\cdot 2+1}{2}\implies \stackrel{improper}{\cfrac{3}{2}} ~\hfill \stackrel{mixed}{1\frac{3}{4}}\implies \cfrac{1\cdot 4+3}{4}\implies \stackrel{improper}{\cfrac{7}{4}} \\\\[-0.35em] ~\dotfill\\\\ \cfrac{3}{2}~~ + ~~\cfrac{7}{4}~~ + ~~\cfrac{7}{4}\implies \cfrac{(2)3~~ + ~~(1)7~~ + ~~(1)7}{\underset{\textit{using this LCD}}{4}}\implies \cfrac{20}{4}\implies 5[/tex]
