Use Kepler's Law of Periods for both planets and equate the \frac{radius^3}{orbital period^2} of the two planets. As \frac{GM}{4\pi^2} is a constant, we can disregard this in this question.
\frac{r_{Alif}^3}{T_{Alif}^2} = \frac{r_{Ba}^3}{T_{Ba}^2} = \frac{(4.00 \times 10^{11})^3}{(8.75...