Calculate the degrees of freedom and the critical values, or cutoffs, assuming a two-tailed test with a p level of 0.05, for each of the following designs: 

a. Data are collected to examine the relation between size of dog and rate of bone and joint health issues. Veterinarians from around the country contributed data on 3113 dogs. 

b. Hours spent studying per week was correlated with credit-hour load for 72 students.