<?php

class SavingAccount

{

    private $balance = 100;

    public function setBalance($balance){

        $this->balance = $balance;

    }

    public function getBalance(){

        return $this->balance;

    }

    public function withdrawal(){}

}

class FixedDipositAccount

{

  private $balance = 20;

  private $maturityPeriod;

  public function setBalance($balance){

      $this->balance = $balance;

  }

  public function getBalance(){

      return $this->balance;

  }

}

​

class IntrestCalculator

{

    public function calculate($account)

    {

        if ($account instanceof SavingAccount) {

            return $account->getBalance() * 3.0;

        } elseif ($account instanceof FixedDipositAccount) {

            return $account->getBalance() * 9.5;

        }

        throw new Exception('Invalid input member');

    }

}

$savingAccount = new SavingAccount();

$savingAccount->setBalance(15000);

$fdAccount = new FixedDipositAccount();

$fdAccount->setBalance(25000);

$intrestCalculator = new IntrestCalculator();

echo $intrestCalculator->calculate($savingAccount);

echo $intrestCalculator->calculate($fdAccount);