Correct answer: 4
According to Kepler's third law, the square of the period of revolution is proportional to the cube of the semi-major axis of the orbit. If the period of A is 8 times that of B, then (T_A / T_B)^2 = (r_A / r_B)^3. Substituting T_A / T_B = 8, we get 8^2 = (r_A / r_B)^3, which simplifies to r_A / r_B = 4.