let's firstly convert the mixed fractions to improper fractions and then add them up.
[tex]\stackrel{mixed}{2\frac{10}{20}}\implies \cfrac{2\cdot 20+10}{20}\implies \stackrel{improper}{\cfrac{50}{20}} ~\hfill \stackrel{mixed}{3\frac{15}{20}}\implies \cfrac{3\cdot 20+15}{20}\implies \stackrel{improper}{\cfrac{75}{20}} \\\\\\ \stackrel{mixed}{5\frac{8}{20}}\implies \cfrac{5\cdot 20+8}{20}\implies \stackrel{improper}{\cfrac{108}{20}} \\\\[-0.35em] ~\dotfill[/tex]
[tex]2\frac{10}{20}-3\frac{15}{20}+5\frac{8}{20}\implies \cfrac{50}{20}-\cfrac{75}{20}+\cfrac{108}{20}\implies \cfrac{50-75+108}{20} \\\\\\ \cfrac{83}{20}\implies 4\frac{3}{20}[/tex]
