Here is the question I'm supposed to answer: The mean income per person in the United States is $50,000, and the distribution of incomes follows a normal distribution. A random sample of 10 residents of Wilm-ington, Delaware, had a mean of $60,000 with a standard deviation of $10,000. At the .05 level of significance, is that enough evidence to conclude that residents of Wilmington, Delaware, have more income than the national average?

.05 significance level

t = (60,000 - 50,000) / (10,000 / square root of 10) = 10,000 / 3164.56 = 3.16

I looked up the t comparison and it's 1.812

I don't understand how to use the t number that I looked up in this example. Can you help explain the concept?