check the picture below.
so first off, let's convert the mixed fractions to "improper fractions", and then sum them up.
[tex]\bf \stackrel{mixed}{3\frac{1}{2}}\implies \cfrac{3\cdot 2+1}{2}\implies \stackrel{improper}{\cfrac{7}{2}}
\\\\\\
\stackrel{mixed}{2\frac{1}{8}}\implies \cfrac{2\cdot 8+1}{8}\implies \stackrel{improper}{\cfrac{17}{8}}
\\\\\\
\stackrel{mixed}{2\frac{1}{2}}\implies \cfrac{2\cdot 2+1}{2}\implies \stackrel{improper}{\cfrac{5}{2}}\\\\
-------------------------------[/tex]
[tex]\bf \cfrac{7}{2}+\cfrac{17}{8}+\cfrac{5}{2}\impliedby \textit{using the LCD of 8}\implies \cfrac{(4\cdot 7)+(1\cdot 17)+(4\cdot 5)}{8}
\\\\\\
\cfrac{28+17+20}{8}\implies \cfrac{65}{8}\implies 8\frac{1}{8}[/tex]
