4) 1/8 + 7/12 - 5/9

$$\frac{1}{8} + \frac{7}{12} - \frac{5}{9} = \frac{1*9}{8*9} + \frac{7*6}{12*6} - \frac{5*8}{9*8} = \frac{9}{72} + \frac{42}{72} - \frac{40}{72} = \frac{9+42-40}{72} = \frac{11}{72}$$
Ответ: $$\frac{11}{72}$$