Use the system expression 'Distance between points', or distance(x1, y1, x2, y2), e.g.
+ System: distance(objectA.X, objectA.Y, objectB.X, objectB.Y) Greater than 100
-> objectA: Move 80 * TimeDelta pixels at angle(objectA.X, objectA.Y, objectB.X, objectB.Y) degrees
-> objectA: Set angle towards objectB