Who can solve this problem ?

Closest Point of Approach

Two spaceships start flying each on its own straight way at different speeds from different locations. You are to determine when

they will be as close to each other as possible. For example, if the first spaceship starts from point (0,0,0) with speed vector

(1,0,0) and the second spaceship starts from (4,2,0) with speed vector (-1,0,0) then after 2 seconds they will be at points

(2,0,0) and (2,2,0) — this is the closest point of their approach.