Bioequivalence and Bioavailability Forum

Dear All,
In the FDA guidance for RSABE for NTI drugs the 90% confidence interval of the ratio of the within subject standard deviation of test product to reference product is required to be less than or equal to 2.5. My question is:

1. How can i calculate this 90% CI on SAS.
   
2. is the F (the value of F distribution) given in the equation:
   
   is the critical F value or else how it could be calculated.

Thanks in advance