6/7 * 14/21 : 5/9 * 4/4

6/7 * 14/21 : 5/9 * 4/4 = (6/7 * 14/21) : 5/9 * 1 = (6 * 14)/(7 * 21) : 5/9 = 84/147 : 5/9 = 84/147 * 9/5 = (84 * 9)/(147 * 5) = 756/735

Сократим дробь на 21:

756/735 = 36/35

Ответ: 36/35