З) 9/13 + 5/26 + 1/78

З) \( \frac{9}{13} + \frac{5}{26} + \frac{1}{78} = \frac{9 · 6}{13 · 6} + \frac{5 · 3}{26 · 3} + \frac{1}{78} = \frac{54}{78} + \frac{15}{78} + \frac{1}{78} = \frac{54+15+1}{78} = \frac{70}{78} = \frac{35}{39} \)