how to Save A random generated number and use it

I want to use a random generated number and save it in a variable. i tried using public float x = Random.Range(minNb, maxNb); but it doesn’t work. Here is the rest of my script.

using System.Collections;
using System.Collections.Generic;
using Unity.Mathematics;
using UnityEngine;

public class Score : MonoBehaviour
{

    public float score = 0;
    public float scoreMulti = 5;
    public float minNb = 100;
    public float maxNb = 200;
    

    // Start is called before the first frame update
    void Start()
    {
        
    }

    // Update is called once per frame
    void Update()
    {
        score += Time.deltaTime * scoreMulti;

        if (score == 70)
        {
           //save random generated number
        }
    }
}

This should work fine. x = Random.Range(minNb, maxNb);

You just gotta make sure to define it as a member variable.

public class Score : MonoBehaviour {
    float x;
    void Awake() {
        x = Random.Range(-100f, 100f);
    }
}