Final answer:
The trip to Vegas served as an extrinsic reward to keep Vivianna motivated.
Step-by-step explanation:
The trip to Vegas served as an extrinsic reward to keep Vivianna motivated. Extrinsic rewards are external incentives or reinforcements that come from outside the individual, such as money or material goods. In this case, the opportunity to go to Las Vegas with her friends was an external reward that motivated Vivianna to save money each week. By setting a goal and knowing she would be rewarded with a fun trip, Vivianna had a tangible reason to stay motivated and save her money.