Rotation follow translation

well after remembering a bit of math, here we go; Iam not sure if diff get the correct distance, the rest is geometry and the transform.Rotate function:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class BasicTrack : MonoBehaviour {
     public Transform TargetObject; //set it on inspector
     public float Angle = Mathf.PI ;//proportional rotation of the second object, default is the same angular translation at diameter 1, multiply by 2 radius to change angular rotation
     float StartPoint = 0;
     float diff; //reusable variable, distance from current x position to previous
 
     void Start () {
         StartPoint = TargetObject.position.x;
     }
     // FixedUpdate is use by physics
     void FixedUpdate () {
         //this if really not work with floats, use a aproximate comparision like Mathf.Abs(Mathf.Abs(StartPoint)-Mathf.Abs(TargetObject.x))<0.01f
         if (StartPoint != TargetObject.position.x) {
             //PI*radius*2 is the distance that a wheel do on a single rotation
             diff = TargetObject.position.x-StartPoint;
             transform.Rotate (Vector3.up, (360/Angle)*diff); 
             StartPoint = TargetObject.position.x;
         }
     }
 }

of course the script will be attached to the object that rotate, the TargetObject is the object moving along the x.

Edited @mustang4484 eliminating the last Mathf.Absu have a unclamped rotation at two directions, to do inverse clockwise replace transform.Rotate (Vector3.up, (360/Angle)*diff); with transform.Rotate (-Vector3.up, (360/Angle)*diff); (note the minus...)

Thank you all, I explained myself badly. I would like that when my Object P move on the right (B) my arrow turn to (B) with degree proportional to start position-b.

It's a similar to @DCordoba but with the inverse clockwise if the player go to -x.

Thank you

If you have a variable for the rotation then you can do something like this,

 float currentRotation, timesDifference, maxAmount;
 
 void Update(){
     transform.eulerAngles.y = currentRotation;
     other.transform.position.x = currentRotation * timesDifference;
     currentRotation = Mathf.Clamp(currentRotation, -maxAmount, maxAmount)
 }

edit: I've just noticed A and B are going in opposite directions.

 other.transform.position.x = -currentRotation * timesDifference;