ok here goes... In a three dimentional environment. i am standing at point (0,0,0) and there is someone else standing at (10,0,0) I start moving with a velocity of (1,2,3)/s and the other guy wants to meet me. I know that he is approaching the point of intersection at 4m/s (that is cumulative). We wind up meeting at the same spot at the same time. My question is how do you get that spot in 3d space and at what time did you meet? This seems that it can be done since we have the initial positions and the velocities. But since you only know the overall velocity of the other guy how do you know how to break it down into the velocities on the X, Y and Z without knowing how much time has passed?