Let's call n the number of days Marika's been training for the race, and the distance she runs on the nth day in meters. After the first day, when n = 1, she runs 100 meters, so
On the second day, she runs an additional 4 meters, on the third day, another 4, and so on. Here's what that looks like mathematically:
It would be easier to write this continued addition as multiplication, in which case those same equations would look like
Notice that, in every case, the number 4 is being multiplied by is 1 less than n. We could even write for our first term that . In general, we can say that
Which is expressed by option B.
(Bonus: What piece of information from this question did we not need to use here?)