4) 7 + 21

1. Convert mixed numbers to improper fractions: $$7\frac{11}{13} = \frac{102}{13}$$, $$21\frac{17}{30} = \frac{647}{30}$$.
2. Find a common denominator (390): $$\frac{102}{13} = \frac{102 \times 30}{13 \times 30} = \frac{3060}{390}$$, $$\frac{647}{30} = \frac{647 \times 13}{30 \times 13} = \frac{8411}{390}$$.
3. Add the fractions: $$\frac{3060}{390} + \frac{8411}{390} = \frac{11471}{390} = 29\frac{101}{390}$$.