Question: how long to cook pork tenderloin at what temp?
Answer: Preheat oven to 400° F. ... 
Season the pork with salt and pepper (add chopped fresh herbs if desired).
Heat oil and brown the pork evenly in a frying pan. ... 
Cook 18-20 minutes or until a thermometer reads an internal temperature of 145° F (While the tenderloin is cooking, begin to prepare the mushroom sauce)