Final answer:
To perform a hypothesis test in this scenario, you should use the t-distribution.
Step-by-step explanation:
To perform a hypothesis test in this scenario, you should use the t-distribution. The t-distribution is used when the sample size is small (typically less than 30) and the population standard deviation is unknown. Since the sample size in this case is 20 and the standard deviation is known, you should use the t-distribution.