#include <bits/stdc++.h>
using namespace std;
inline long long read() {
  long long x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = (x << 1) + (x << 3) + ch - '0';
    ch = getchar();
  }
  return x * f;
}
struct edge {
  int v, w, next;
} e[300005 << 1];
int head[300005], k;
inline void add(int u, int v, int w) {
  e[k] = (edge){v, w, head[u]};
  head[u] = k++;
}
int n, q;
long long f[300005], a[300005];
inline void dp(int u, int fa) {
  f[u] = a[u];
  for (int i = head[u]; ~i; i = e[i].next) {
    int v = e[i].v;
    if (v == fa) continue;
    dp(v, u);
    if (f[v] - e[i].w - e[i ^ 1].w > 0) f[u] += f[v] - e[i].w - e[i ^ 1].w;
  }
}
int p[300005][30];
long long F1[300005][30], F2[300005][30], g[300005];
int dep[300005];
inline void dfs(int u, int fa) {
  dep[u] = dep[p[u][0] = fa] + 1;
  for (int i = 1; i <= 25; ++i) {
    p[u][i] = p[p[u][i - 1]][i - 1];
    F1[u][i] = F1[u][i - 1] + F1[p[u][i - 1]][i - 1] - f[p[u][i - 1]];
    F2[u][i] = F2[u][i - 1] + F2[p[u][i - 1]][i - 1] - f[p[u][i - 1]];
  }
  for (int i = head[u]; ~i; i = e[i].next) {
    int v = e[i].v;
    if (v == fa) continue;
    F1[v][0] = f[v] + f[u] - e[i ^ 1].w;
    if (f[v] - e[i].w - e[i ^ 1].w > 0) F1[v][0] -= f[v] - e[i].w - e[i ^ 1].w;
    F2[v][0] = f[v] + f[u] - e[i].w;
    if (f[v] - e[i].w - e[i ^ 1].w > 0) F2[v][0] -= f[v] - e[i].w - e[i ^ 1].w;
    g[v] = max(g[v], g[u] + F1[v][0] - e[i].w - f[v]);
    dfs(v, u);
  }
}
inline long long Query(int u, int v) {
  long long ans = 0;
  int a = u, b = v;
  if (dep[u] > dep[v]) {
    for (int i = 25; i >= 0; --i)
      if (dep[p[u][i]] >= dep[v]) {
        ans += F1[u][i] - f[u];
        u = p[u][i];
      }
    if (u == v) return ans + f[a] + g[u];
  } else {
    for (int i = 25; i >= 0; --i)
      if (dep[p[v][i]] >= dep[u]) {
        ans += F2[v][i] - f[v];
        v = p[v][i];
      }
    if (u == v) return ans + f[b] + g[u];
  }
  for (int i = 25; i >= 0; --i)
    if (p[u][i] != p[v][i]) {
      ans += F1[u][i] - f[u];
      ans += F2[v][i] - f[v];
      u = p[u][i];
      v = p[v][i];
    }
  return ans + F1[u][0] - f[u] + F2[v][0] - f[v] - f[p[u][0]] + f[a] + f[b] +
         g[p[u][0]];
}
int main() {
  n = read(), q = read();
  for (int i = 1; i <= n; ++i) a[i] = read();
  memset(head, -1, sizeof(int) * (n + 5));
  for (int i = 1; i < n; ++i) {
    int u = read(), v = read();
    long long w = read();
    add(u, v, w);
    add(v, u, w);
  }
  dp(1, 0);
  dfs(1, 0);
  while (q--) {
    int u = read(), v = read();
    printf("%lld\n", Query(u, v));
  }
  return 0;
}
