Question

In a research report, Richard H. Weindruch of
the UCLA Medical School claims that mice with an
average life span of 32 months will live to be about 40
months old when 40% of the calories in their diet are
replaced by vitamins and protein. Is there any reason
to believe that μ < 40 if 64 mice that are placed on
this diet have an average life of 38 months with a standard deviation of 5.8 months?