So, I didn't quite understand your question clearly, but I'll try my best to answer it.
So, the first question is quite simple: Did the runner have a % decrease in his time or an increase. Well, 7:45 is minor than 5:51. So, his time decreased.
2nd question: The percent of change. Well, first things first 7:45 has 2 different units, wich are minutes and seconds, I suppose. Same goes for 5:51. So let's put everything in seconds. multiply both the 7 and 5 for 60(for every minute has 60 seconds.)
That means: 7*60= 420+45 = 465. 5*60=300+51=351.
Now, let's do the math itself: 465 -> 100% 351 -> x% Is equal to about 75,5% How much did it decrease then? (75,5-100)%= 24,5%, approximately
