Returning counting result from Firebase Query

I try to get the amount of rows in my Firebase.
But is says cannot find counter in scope on line return counter.

extension FourthTabFirstView: UITableViewDataSource {
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        
        let ref = database.child("placeID")
        ref.observe(.value, with: { (snapshot: DataSnapshot!) in
        print(snapshot.childrenCount)
        let counter = snapshot.childrenCount
        })

        return counter
    }
    ......
    
}

>Solution :

1- Declare this instance variable

var counter = 0

2- This should be inside viewDidLoad

let ref = database.child("placeID")
ref.observe(.value, with: { [weak self] (snapshot: DataSnapshot!) in
   print(snapshot.childrenCount)
   self?.counter = snapshot.childrenCount
   self?.tableView.reloadData()
})

3- Change numberOfRowsInSection

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
   return counter
 }