Airplanes A and B are flying with constant velocity in the same vertical plane at angles $$30^\circ$$ and $$60^\circ$$ with respect to the horizontal respectively as shown in figure. The speed of A is $$100 \sqrt 3 ms^{−1}$$. At time t = 0 s, an observer in A finds B at a distance of 500 m. This observer sees B moving with a constant velocity perpendicular to the line of motion of A. If at $$t = t_0$$, A just escapes being hit by B, $$t_0$$ in seconds is