#include <bits/stdc++.h>
using namespace std;
long long n, q;
long long a[300005], dp_child[300005], dp_par[300005];
long long now, tin[300005], tout[300005], up[300005][19], val[300005][19],
    val2[300005][19];
vector<pair<long long, long long> > g[300005];
map<pair<long long, long long>, long long> mp;
void get_child(long long u, long long p) {
  for (auto e : g[u])
    if (e.first != p) {
      long long v = e.first, w = e.second;
      get_child(v, u);
      dp_child[u] += max(0ll, dp_child[v] + a[v] - 2 * w);
      mp[{v, u}] = max(0ll, dp_child[v] + a[v] - 2 * w);
    }
}
void get_par(long long u, long long p) {
  for (auto e : g[u])
    if (e.first != p) {
      long long v = e.first, w = e.second;
      long long t = max(0ll, dp_child[u] - mp[{v, u}]);
      dp_par[v] = max(0ll, dp_par[u] + a[u] - 2 * w + t);
      get_par(v, u);
    }
}
void dfs(long long u, long long p) {
  tin[u] = ++now;
  for (long long i = 1; i <= 18; i++) {
    up[u][i] = up[up[u][i - 1]][i - 1];
    val[u][i] = val[u][i - 1] + val[up[u][i - 1]][i - 1];
    val2[u][i] = val2[u][i - 1] + val2[up[u][i - 1]][i - 1];
  }
  for (auto e : g[u])
    if (e.first != p) {
      long long v = e.first, w = e.second;
      up[v][0] = u;
      val[v][0] = a[v] - w + dp_child[v];
      val2[v][0] = mp[{v, u}];
      dfs(v, u);
    }
  tout[u] = now;
}
bool is_ancestor(long long u, long long v) {
  return (tin[u] <= tin[v] && tout[u] >= tout[v]);
}
long long lca(long long u, long long v) {
  if (is_ancestor(u, v)) return u;
  if (is_ancestor(v, u)) return v;
  for (long long i = 18; i >= 0; i--)
    if (!is_ancestor(up[u][i], v)) u = up[u][i];
  return up[u][0];
}
long long solve(long long u, long long v) {
  long long r = lca(u, v), res = 0;
  for (long long i = 18; i >= 0; i--) {
    if (!is_ancestor(up[u][i], r)) {
      res += val[u][i] - val2[u][i];
      u = up[u][i];
    }
    if (!is_ancestor(up[v][i], r)) {
      res += val[v][i] - val2[v][i];
      v = up[v][i];
    }
  }
  if (u != r) {
    res += val[u][0];
    res -= mp[{u, r}];
  }
  if (v != r) {
    res += val[v][0];
    res -= mp[{v, r}];
  }
  return res + a[r] + dp_child[r] + dp_par[r];
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cin >> n >> q;
  for (long long i = 1; i <= n; i++) cin >> a[i];
  for (long long i = 1; i <= n - 1; i++) {
    long long u, v, w;
    cin >> u >> v >> w;
    g[u].push_back({v, w});
    g[v].push_back({u, w});
  }
  get_child(1, 0);
  get_par(1, 0);
  tin[0] = -1000000000000000000;
  tout[0] = 1000000000000000000;
  dfs(1, 0);
  while (q--) {
    long long u, v;
    cin >> u >> v;
    cout << solve(u, v) << "\n";
  }
}
