<?php
class saskaita{
    public $balance;
    public static $incomeLimit = 500;
    public static $outcomeLimit = 800;

    public function saskaita($balance){
        $this->balance = $balance;
    }
    public function getBalance(){
        return $this->balance;
    }

    public function addToBalance($income){
        if($this->incomeLimit < $income){
            $this->balance += $income;
        }
    }
    public function removeFromBalance($outcome){
        if($this->outcomeLimit > $outcome && $outcome < $this->balance){
            $this->balance -= $outcome;
        }
    }
}

$sask = new saskaita(5000);
$sask->addToBalance(400);
echo $sask->getBalance();
$sask->removeFromBalance(100);
echo $sask->getBalance();