#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <tuple>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <deque>
#include <bitset>
#include <cctype>
#include <functional>
#include <cassert>
using namespace std;

#define REP(i, n) for (int i = 0; i < (int)(n); i++)

using ll = long long;
using ull = unsigned long long;
using Matrix = std::vector<std::vector<ll>>;
const int inf = 1000000000;
const ll INF = 1000000000000000000;
const ll mod = 998244353;
const ull mod_hash = (1UL << 61) - 1;
const std::vector<int> dx = {0, 1, 0, -1, 1, 1, -1, -1};
const std::vector<int> dy = {1, 0, -1, 0, 1, -1, 1, -1};

int main(){
  int T; cin >> T;
  while(T--){
    ll N, X; cin >> N >> X;
    ll target = 0;
    REP(i, N) {
      ll c; cin >> c;
      target += (1LL << c);
    }
    ll ans = 0;
    ll now = 0;
    REP(i, 61){
      if((X >> i) & 1){
        now += (1LL << i);
      }
      
      ll tmp = (1LL << 62);
      if((target >> i) & 1 && !((now >> i) & 1)){
        tmp = min(tmp, (1LL << i) - now);
        if(now < X) tmp = min(tmp, now + 1);
        ans = max(ans, 2 * tmp);
      }
    }
    cout << ans << endl;
  }
  return 0;
}