There are 3600 sec in any given hour. there for if take any speed given in miles per hour and divide that number ino 3600, the result is the number of seconds to travel one mile. EX. if you are traveling at 60mph then most people know that is should take one min, or 60 sec, to get from one mile marker to the next, this has been a standard of checking your speedometer that truckers have used for years. so 3600/60=60. So if you divide 3600 by S the result would be T, or if you divide 3600 by S + 5 the result would be T - 11. By substituting T in terms of S you get and equations that can be solved for S. However my equation solving skills are very rusty. I am sure yours are fresh and keen so see what you can do with this and please let me know how it worked