21) (56/98)⁷ : (20/70)⁷
(56/98)⁷ : (20/70)⁷ = (4/7)⁷ : (2/7)⁷ = (4/7)⁷ · (7/2)⁷ = (4⁷ · 7⁷)/(7⁷ · 2⁷) = 4⁷/2⁷ = (2²)⁷/2⁷ = 2¹⁴/2⁷ = 2^(14-7) = 2⁷ = 128
Ответ: 128