#include <bits/stdc++.h>
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int MAXN = 4e5 + 100;
int N, Q, a[MAXN];
vector<pair<int, int> > g[MAXN];
const int MAXK = 22;
int depth[MAXN], pa[MAXK][MAXN];
long long answer[MAXK][MAXN], edgesum[MAXK][MAXN];
long long dp[MAXN];
void dfs(int v = 0, int p = -1) {
  pa[0][v] = p;
  dp[v] = a[v];
  for (auto [u, w] : g[v]) {
    if (u ^ p) {
      depth[u] = depth[v] + 1;
      dfs(u, v);
      dp[v] = max(dp[v], dp[v] + dp[u] - 2 * w);
    }
  }
  for (auto [u, w] : g[v]) {
    if (u ^ p) {
      edgesum[0][u] = -w;
      answer[0][u] = dp[v] - max(0ll, dp[u] - 2 * w);
    }
  }
}
long long dp2[MAXN];
void dfs2(int v = 0, int p = -1) {
  for (auto [u, w] : g[v]) {
    if (u ^ p) {
      dp2[u] = max(dp2[u], dp2[v] + answer[0][u] - 2 * w);
      dfs2(u, v);
    }
  }
}
void solve() {
  cin >> N >> Q;
  for (int i = (0); i < (N); i++) cin >> a[i];
  for (int i = (0); i < (N - 1); i++) {
    int u, v, w;
    cin >> u >> v >> w;
    --u, --v;
    g[u].push_back({v, w});
    g[v].push_back({u, w});
  }
  dfs();
  dfs2();
  for (int k = (0); k < (MAXK - 1); k++) {
    for (int i = (0); i < (N); i++) {
      if (pa[k][i] == -1) {
        pa[k + 1][i] = pa[k][i];
        answer[k + 1][i] = answer[k][i];
        edgesum[k + 1][i] = edgesum[k][i];
      } else {
        pa[k + 1][i] = pa[k][pa[k][i]];
        answer[k + 1][i] = answer[k][i] + answer[k][pa[k][i]];
        edgesum[k + 1][i] = edgesum[k][i] + edgesum[k][pa[k][i]];
      }
    }
  }
  for (int q = (0); q < (Q); q++) {
    int u, v;
    cin >> u >> v;
    --u, --v;
    if (u == v) {
      cout << dp[v] + dp2[v] << "\n";
      continue;
    }
    long long ans = 0;
    if (depth[u] < depth[v]) swap(u, v);
    int x = u, diff = depth[u] - depth[v];
    for (int k = (MAXK - 1); k >= (0); k--) {
      if (diff >> k & 1) {
        ans += answer[k][x];
        ans += edgesum[k][x];
        x = pa[k][x];
      }
    }
    if (x == v) {
      ans += dp[u] + dp2[v];
      cout << ans << "\n";
      continue;
    }
    ans += dp[u];
    ans += dp[v];
    u = x;
    for (int k = (MAXK - 1); k >= (0); k--) {
      if (pa[k][u] != pa[k][v]) {
        ans += answer[k][u];
        ans += edgesum[k][u];
        ans += answer[k][v];
        ans += edgesum[k][v];
        u = pa[k][u];
        v = pa[k][v];
      }
    }
    ans += answer[0][u];
    ans += answer[0][v];
    ans -= dp[pa[0][u]];
    ans += edgesum[0][u];
    ans += edgesum[0][v];
    ans += dp2[pa[0][u]];
    cout << ans << "\n";
  }
}
int main() {
  ios_base::sync_with_stdio(false), cin.tie(nullptr);
  solve();
  return 0;
}
