How do I get previous pos (X,Y) from current Angle of Motion

The object I am trying to figure out the previous location of is a Bullet that uses the Bullet behavior.

An NPC needs to be able to move a set distance (say 500 pixels) toward the point (X,Y) where the bullet was created/fired from (this NPC uses Pathfinding).

I am trying to do this without taking into account the current location of the bullet (my check for the Bullet position doesn't happen every tick due to the sheer amount of bullets on the game screen at any time). So my question is - is this even possible? We know the location of the NPC and the Angle of Motion + Distance Traveled for the bullet.. how do we determine the X and Y that the NPC should move toward?

Thanks.

give the npc two instance variables (x and y) when bullet (in question) is created store its x and y in npc.x and npc.y so you always know where you want to go ?

RamPackWobble What X & Y would I then move the NPC to, to be within 500 pixels of the Bullets creation point?

how about running a

every now and again...

if distance (npc.x,npc,y,npcrememberedx,npcrememberedy)<500 then stop movement ?