4) 8 5/9 + 7 3/4 + 12 7/12 .

4) $$8 \frac{5}{9} + 7 \frac{3}{4} + 12 \frac{7}{12} = (8 + 7 + 12) + (\frac{5}{9} + \frac{3}{4} + \frac{7}{12}) = 27 + (\frac{5 \cdot 4}{9 \cdot 4} + \frac{3 \cdot 9}{4 \cdot 9} + \frac{7 \cdot 3}{12 \cdot 3}) = 27 + (\frac{20}{36} + \frac{27}{36} + \frac{21}{36}) = 27 + \frac{68}{36} = 27 + \frac{17}{9} = 27 + 1 \frac{8}{9} = 28 \frac{8}{9}$$

Ответ: $$28 \frac{8}{9}$$