error CS0019: Operator `<=' cannot be applied to operands of type `UnityEngine.Vector3' and `float'

Hello, I was trying to make an enemy do an attack animation when they got close enough to the player, but I have gotten caught into a snag. When using comparison operators to compare Vector3 and float values, its not going to work out is what I found out. I tried looking in the documentation but I feel like I'm going in there blindly and don't know where to start really to solve this. I would really appreciate any help from people and take advises they would give.

here is my code that I was working on that started causing me trouble:

  using UnityEngine;
     using System.Collections;
     
     public class EnemyAIMelee : MonoBehaviour 
     {
         public float targetDistance = 20.0f;
         public float attackDistance = 10.0f;
     
         public float enemySpeed = -40.0f;
         public float chaseSpeed = 0.0f;
     
         private bool spawningIn = true;
         private bool unlockAI = false;
         public GameObject playerCharacterManager;
     
         void Start()
         {
             playerCharacterManager = GameObject.FindGameObjectWithTag ("PlayerCharacterManager");
         }
     
         // Update is called once per frame
         void LateUpdate () 
         {
             SpawnIn ();
             MovingAI ();
             AttackAI ();
         }
     
         void SpawnIn()
         {
             if (spawningIn == true) 
             {
                 GameObject plane = GameObject.FindGameObjectWithTag("PlayerPlane");
                 if (transform.position.z - plane.transform.position.z <= targetDistance) 
                 {
                     SendMessage("EnemyMovingAnimation", false);
                     transform.parent = plane.transform;
                     unlockAI=true;
                     spawningIn = false;
                 }
                 
                 else
                 {
                     SendMessage("EnemyMovingAnimation", true);
                     transform.position += transform.forward*enemySpeed*Time.deltaTime;
                 }
             }
         }
     
         void MovingAI()
         {
             if(unlockAI == true)
             {
                 float chasingSpeed = chaseSpeed * Time.deltaTime;
                 //transform.LookAt(playerCharacterManager);
                 transform.position = Vector3.MoveTowards (transform.position, playerCharacterManager.transform.position, chasingSpeed);
                 SendMessage ("EnemyMovingAnimation", true);
 
 //This IF STATEMENT IS THE PROBLEM
                 if(transform.position - playerCharacterManager.transform.position <= attackDistance)
                 {
                     AttackAI ();
                 }
             }
         }
     
         void AttackAI()
         {
             SendMessage ("EnemyAttackAnimation", true);
         }
     }