Add bonus to score

Hi, so I’m new to unity and C# and am trying to add a bonus to my score (score measures the players z position) and really don’t really know how so a little help would be really nice. Heres what I have

using UnityEngine;
using UnityEngine.UI;

public class Score : MonoBehaviour
{
    public Transform player;
    public Text scoreText;
    private int _score;
    private int baseScore;




    // Update is called once per frame
    void Update()
    {
        scoreText.text = player.position.z.ToString("0");
        if (player.position.y >= 2.5)
        {
            _score += 50;
            scoreText.text = _score.ToString();
            Debug.Log(scoreText.text);
            // scoreText.text = player.position.z.ToString(scoreText.text + 100);

            // scoreText.text = scoreText.text + player.position.z.ToString();
        }

        // Debug.Log(scoreText.text);
    }
}

What happens is that it literally adds 50 to the end. Good luck and thank you!

using UnityEngine;
using UnityEngine.UI;

 public class Score : MonoBehaviour
 {
     public Transform player;
     public Text scoreText;
     private float score;
     private float scoreBonus;
 
     // Update is called once per frame
     void Update()
     {
         score = player.position.z ;
         if (player.position.y >= 2.5)
             scoreBonus = 50;

         scoreText.text = (score + scoreBonus).ToString("0");
     }
 }