73,569 a rounded to the nearest 10,000

You look at the next digit to the ten thousands place, in this case it is 3, and 3 is smaller than 5, so you do nothing to the ten thousands and change all else to zero

the rules of approx is
5 or larger-+1 to place approximating and change all else to 0

4 or smaller - Do nothing to place approximating and change all else to zero

Yes you do, so £1973.09 - £1473.50 = £499.59 so tim overpaid £499.59 .hope this ; )