4. Вычислите: 1/3 + (2/3)^2 ÷ 2 · 8/21

1/3 + (4/9) ÷ 2 · 8/21 = 1/3 + 4/9 ÷ 2 · 8/21 = 1/3 + (2/9) · 8/21 = 1/3 + 16/189 = 63/189 + 16/189 = 79/189.