A hunter is riding an elephant of height 4m moving in straight line with uniform speed of 2m/s. A deer running with a speed V at a distance of (4squaroot5)m moving perpendicular to direction of motion of the elephant. If hunter can throw his spear with a speed 10m/s relative to elephant, then at what angle to its direction of motion must he thrown w.r.t elephant his spear horizontally for a successfull hit. Find also the speed V of deer.