Final answer:
Sammi completed the dirt bike race in 35 minutes, which is calculated by taking the finishing time of Ali and subtracting the time Sammi arrived before Ali.
Step-by-step explanation:
To determine how many minutes it took for Sammi to finish the race, we need to use the information provided about the times in which each participant finished and calculate backwards from the known times.
Zack finished the race in 38 minutes. Ali finished 9 minutes after Zack, which means Ali finished in 38 minutes + 9 minutes = 47 minutes. Sammi came in 12 minutes before Ali, so Sammi finished in 47 minutes - 12 minutes = 35 minutes.