A regular function vs arrow function callback

An account object has a balance property and a method schedule to simulate a credit and a debit after scheduled time:

// account has $100 balance at start.
var account = { balance: 100 };

account.schedule = function () {

 /* Schedule a $100 credit after 1/2 second.
    Use arrow function for timer callback.*/
 setTimeout( () => {      
   // Credit $100 
   this.balance += 100;       

   /* Schedule a $200 debit after 
      1/2 second. Use regular function
      for timer callback.*/
   setTimeout( function() { 
    // Debit $200
    this.balance -= 200;
   }, 500 );            

 }, 500 );  

};

The account object is created with $100 balance. The schedule method schedules a $100 credit after a 1/2 second (500ms) timeout. The callback arrow function credits $100 and then schedules a $200 credit after another 1/2 second (500ms) timeout, notice that this time the timer callback function is a regular function.

This question highlights a very important difference between arrow function and regular function related to how 'this' is bound. Let's call the account.schedule and check the balance after 2 seconds.

// Call schedule() to schedule credit/debit
account.schedule();

// Check balance after 2 seconds
setTimeout( function() { 
    console.log(account.balance);           
}, 2000 );

What do you think would be logged as account.balance (after 2 seconds) above?