A cannon fires successively two shells with velocity 250 m/s. The first at an angle 60⁰ and the second at the angle 45⁰ to the horizontal, the azimuth being the same. Find the time interval between their firing so that the two shells collide in air. Assume no air friction. 

(in secs) (take g = 10m/s²) $(take\sqrt{2}=1.414\&\sqrt{3}=1.732)$