Big Yellow said:
...which one do I pay for?
The "set fine" should be the higher of the two. This is the "actual" fine payable for the offense you are charged with. If you fight the ticket and lose, that's what you'll be charged (plus possible extra court fees).
If you admit that you were legitimately caught, pay the lower amount by the deadline and save a few bucks up-front. However, get ready for your insurance rates to go balistic!
If there's any chance that you're innocent, you might consider fighting the ticket to protect your driving record. There have been numerous threads on this process in the past but there are ways to improve your odds of winning. If you've already got some offenses on your record, you might want to get some professional help (legal, not mental) because too many moving violations can suspend your license or permit your insurance company not to renew your policy.
Zog.