#include<cstdio>

 #include<iostream>

 #include<algorithm>

 #include<cstring>

 #include<cmath>

 #include<queue>

 #include<map>

 using namespace std;

 #define MOD 1000000007

 const int INF=0x3f3f3f3f;

 const double eps=1e-;

 typedef long long ll;

 #define cl(a) memset(a,0,sizeof(a))

 #define ts printf("*****\n");

 const int MAXN=;

 int n,m,tt;

 /*

 * Kruskal算法求MST

 */

 const int MAXM=;//最大边数

 int tol;//边数，加边前赋值为0

 struct Edge

 {

     int to,next;

 }edge[MAXM];

 int head[MAXN],tot;

 void init()

 {

     tot = ;

     memset(head,-,sizeof(head));

 }

 void addedge(int u,int v)

 {

     edge[tot].to = v; edge[tot].next = head[u];

     head[u] = tot++;

 }

 bool mp[MAXN][MAXN];

 double dp[MAXN][MAXN];

 /*

 * Prim求MST

 * 耗费矩阵cost[][]，标号从0开始，0~n-1

 * 返回最小生成树的权值，返回-1表示原图不连通

 */

 int vis[MAXN];

 double lowc[MAXN];

 double Prim(double cost[][MAXN],int n)//点是0~n-1

 {

     double ans=;

     memset(vis,false,sizeof(vis));

     vis[]=-;

     int last[MAXN];

     last[]=;

     for(int i=;i<n;i++)lowc[i]=cost[][i];

     for(int i=;i<n;i++)

     {

         double minc=INF;

         int p=-;

         for(int j=;j<n;j++)

             if(vis[j]!=-&&minc>lowc[j])

             {

                 minc=lowc[j];

                 p=j;

             }

         if(minc==INF)return -;//原图不连通

         mp[vis[p]][p]=mp[p][vis[p]]=;

         addedge(vis[p],p);

         addedge(p,vis[p]);

         ans+=minc;

         vis[p]=-;

         for(int j=;j<n;j++)

             if(vis[j]!=-&&lowc[j]>cost[p][j])

             {

                 vis[j]=p;

                 lowc[j]=cost[p][j];

             }

     }

     return ans;

 }

 int x[MAXN],y[MAXN];

 double dist[MAXN][MAXN];

 double dis(int i,int j)

 {

     return sqrt((double)(x[i]-x[j])*(double)(x[i]-x[j])+(double)(y[i]-y[j])*(double)(y[i]-y[j]));

 }

 double dfs(int cur,int u,int fa){

         double res=(double)INF;

         for(int i=head[u];i!=-;i=edge[i].next){

             int v=edge[i].to;

             if(v==fa)continue;

             double tmp=dfs(cur,v,u);

             dp[u][v]=dp[v][u]=min(tmp,dp[u][v]);

             res=min(res,tmp);

         }

         if(fa!=cur){

             res=min(res,dist[cur][u]);

         }

         return res;

     }

 int main()

 {

     int i,j,k,ca=;

     #ifndef ONLINE_JUDGE

     freopen("1.in","r",stdin);

     #endif

     scanf("%d",&tt);

     int val;

     while(tt--)

     {

         init();

         tol=;

         scanf("%d%d",&n,&val);

         cl(dist);

         for(i=;i<n;i++)

         {

             scanf("%d%d",x+i,y+i);

         }

         for(i=;i<n;i++)

         {

             for(j=;j<n;j++)

             {

                 dist[i][j]=dist[j][i]=dis(i,j);

             }

         }

         cl(mp);

         double sumw=Prim(dist,n);

         double Max=sumw;

         for(int i=;i<n;i++)

                 for(int j=i;j<n;j++)

                     dp[i][j]=dp[j][i]=(double)INF;

         for(i=;i<n;i++)

         {

             dfs(i,i,-);

         }

         for(i=;i<n;i++)  //枚举每条边

         {

             for(j=i+;j<n;j++)

             {

                 if(mp[i][j])    Max=max(Max,sumw-dist[i][j]+dp[i][j]);

             }

         }

         printf("%.2lf\n",Max*val);

     }

 }