Help me in solving EQUALARRAY problem

help
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My issue

My code

import java.util.Scanner;

class Codechef {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int m = scanner.nextInt();
        int n = scanner.nextInt();
        int x = scanner.nextInt();

        int[][] matrix = new int[m][n];
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                matrix[i][j] = scanner.nextInt();
            }
        }

        int result = findMinimumOperations(matrix, x);
        System.out.println(result);
    }

    private static int findMinimumOperations(int[][] matrix, int x) {
        int m = matrix.length;
        int n = matrix[0].length;

        // Check if it's possible to make all elements equal
        int remainder = matrix[0][0] % x;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (matrix[i][j] % x != remainder) {
                    return -1; // It's not possible to make all elements equal
                }
            }
        }

        // Calculate the minimum number of operations
        int target = matrix[0][0];
        int operations = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                int diff = Math.abs(matrix[i][j] - target);
                operations += diff / x;
            }
        }

        return operations;
    }
}

Problem Link: EQUALARRAY Problem - CodeChef

Please help me the understand the problem i am unable to understand.