iit jee physics 2014 kinematics

iit jee physics 2014 kinematics
Airplanes A and B are flying with constant ve- locity in the same vertical plane at angles 30° and 60° with respect to the horizontal respectively as shown in the figure. The speed of A is 100/3 m/s. At time t=0s, 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 = to, A just escapes being hit by B, to in seconds is