Answer:
t = -5.4548 with 17 degrees of freedom
Step-by-step explanation:
The t-test statistic can be calculated as:

Where x is the average cholesterol of the sample, μ is the average cholesterol to test, s is the standard deviation and n is the size of the sample. So, the test statistic is

This test statistic is with (n - 1) degrees of freedom.
So, the answer t = -5.4548 with 17 degrees of freedom