Answer: Hello there!
we know that on Tuesday, Jennie finished her sprint 0.305 seconds faster than on Monday, and we want to model this with math.
If we define x as the time in which she finished ger sprint on Monday, we can write the time for Tuesday as x - 0.305s
this is because she finished her sprint 0.305 seconds "faster", this means that she finished it in less time, so you need to subtract this number to the previous time.
Then the meaning of 0.305 is the amount of time that you need to subtract from the previous time, in order to get the actual time that she needs to finish the sprint.