Ответ:

Пошаговое объяснение:

3)

29/42 - a - 13/42 = 11/42

16/42 - a = 11/42

a = 16/42 - 11/42

a = 5/42

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4)

x/72 = 21/72 + 13/72

x/72 = 34/72

x = 34