A normal white blood count is assumed to be approximately 8 (thousands) cell per cc of blood. A random sample of 15 employees of a nuclear plant yielded a mean white count of 7.81 with a population...

A normal white blood count is assumed to be approximately 8 (thousands) cell per cc of blood. A random sample of 15 employees of a nuclear plant  yielded a mean white count of 7.81 with a population standard deviation of 0.872 (in thousands.) Is there significant evidence that the mean white
count is lower for plant employees using a significance level of 0.05?