[dolphinsea14]

Hair found at the scene of a crime is analyzed and compared with hair belonging to a suspect.  Using atomic absorption analysis, a technique known to have a true (or population) standard deviation of 12.00 ppm zinc, the following results were obtained.
Hair at crime:196, 204  ppm Zn
Hair from suspect:193, 188, 195, 199  ppm Zn
Using the method of comparison of means can you deduce that the suspect is guilty of the crime?

I think I should use t-test for this task.
But I am not sure where to use the standard deviation of the technique in my calculations. Can you help me?