import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int t = sc.nextInt();
        while (t-- > 0) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            int count = 0;
            if(a % b == 0){
                System.out.println(0);
            }
            else{
                while(a % b != 0){
                    a += 1;
                    count++;
                }
                System.out.println(count);
            }
        }
    }
}

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NQoxMCA0CjEzIDkKMTAwIDEzCjEyMyA0NTYKOTIgNDYK

5
10 4
13 9
100 13
123 456
92 46