JAVA SOLUTION

import java.io.; import java.util.;

public class Solution {

public static void validator(String word){

    // First character must be a letter : ^[a-zA-Z]

    // Following characters can be either letters , numbers or _ : [a-zA-Z_0-9]

    // Must have 8-30 characters so after the first validation to the last character 
    // can have 7 to 29 =  {7,29}$

    if (word.matches("^[a-zA-Z][a-zA-Z_0-9]{7,29}$")) {
        System.out.println("Valid");
    }
    else{
       System.out.println("Invalid"); 
    }

}

public static void main(String[] args) {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */

    Scanner sc = new Scanner(System.in);
    int numWords = sc.nextInt();

    sc.nextLine();

    for (int i = 0; i < numWords; i++) {
        String word = sc.nextLine();
        validator(word);

    }

    sc.close();


}

}