5) \(\frac{5}{12} + \frac{5}{21}\) = \(\frac{35}{84} + \frac{20}{84}\) = \(\frac{55}{84}\)

5) \( \frac{5}{12} + \frac{5}{21} = \frac{5 \cdot 7}{12 \cdot 7} + \frac{5 \cdot 4}{21 \cdot 4} = \frac{35}{84} + \frac{20}{84} = \frac{35+20}{84} = \frac{55}{84} \)