Answer:
4th. as it had UNIQUE values for every x
unlike rest 3,
like 2nd has two values of 3, not a function
First is 7 second is 8 third is 3
2nd attempt carries a price of 6% extra, so (6/100) * 548 is 32.88, so 548 + 32.88, the price is 580.88.
for the 3rd attempt 6% extra of that, (6/100) * 580.88, is 34.8528, so the price is 615.7328.
4th attempt is 6% extra of that, (6/100) * 615.7328, 36.943968, adding that will give us 652.676768.