Final answer:
Sheila's motivation in the provided sentence is the goal of completing a marathon, evident through her purchase of running shoes and consistent training on the school track.
Step-by-step explanation:
When analyzing the sentence about Sheila, who wants to complete a marathon, her motivation is the desire to achieve the goal of finishing the marathon. This is evident as she invests in new running shoes and dedicates time to training on the school track. The acts of buying new running shoes, running the school track, and timing her runs are all strategic behaviors influenced by her underlying motivation which is completing a marathon. These actions are in line with various theories of motivation, which suggest that our behaviors are directed by our wants or needs to achieve certain goals. Sheila's effort exemplifies a mix of intrinsic motivation, as she may enjoy running and the personal satisfaction of achieving a goal, as well as extrinsic motivation, which could include the accolades that come with marathon completion.