checkOut(id, stationName, t) {
    const user = this.stationSystem[id];
    user[1] = stationName;
    user[3] = t;
    const stationHash = `${user[0]}-${user[1]}`;
    if (this.averageTime[stationHash]) {
      this.averageTime[stationHash][0] += 1;
      this.averageTime[stationHash][1] += user[3] - user[2];
    } else {
      this.averageTime[stationHash] = [];
      this.averageTime[stationHash][0] = 1;
      this.averageTime[stationHash][1] = user[3] - user[2];
    }
  }
Time O(1) | Space O(1)
Records the check-out time and station for a user, and calculates the average time.
@param {number} id - User ID
@param {string} stationName - Check-out station name
@param {number} t - Check-out time
@return {void}