A useful exchange rate / currency calculator site is linked on the website when you are purchasing S2.

http://www.xe.com/

The currency of 24 GBP (Pounds) is used, not Euros.

Quote from https://www.liveforspeed.net/?page=shop :

All prices are in UK Pounds. If you want to know the prices in your own currency, you can look it up at www.xe.com (a currency conversion website).

Quote from www.xe.com :

24.00 GBP = 47.2175 USD

Learn to use Google, it will save the trouble of posting these things

You can also use google. Type this into the search box: 24 GBP in USD

I am in USA too. I paid my S2 license using paypal. It is calculated around 48 bucks

If you're writing a postal order in foreign currency, surely they would make the postal order for 24 GBP, do the conversion when you're there using the day's exchange rate and then charge you the correct amount in your home currency (plus conversion fee etc)? That's what they did last time I had to use Western Union to pay for an ebay win from a non-Paypal seller in the US.

To write an order in USD and just hope it should be enough doesn't make sense. I mean, what if you wrote an order for $32.10 (or whatever it was), posted it and it turned out you were 15c short when the order actually got there? Wait till you get to the post office, ask for a postal order for 24 pounds and you won't have to do anything but pay for it and send it.