a. $\frac{7}{9}$ + $\frac{9}{10}$
= $\frac{70}{90}$ + $\frac{81}{90}$ = $\frac{151}{90}$
b. $\frac{5}{6}$ + $\frac{7}{8}$
= $\frac{20}{24}$ + $\frac{21}{24}$ = $\frac{41}{24}$
c. $\frac{3}{5}$ + $\frac{1}{2}$ + $\frac{3}{10}$
= $\frac{6 + 5 + 3}{10}$ = $\frac{14}{10}$ = $\frac{7}{5}$