How long should I cook this pork tenderloin?

I have a pork tenderloin that is approximately 3 lb. I don’t have a meat thermometer, so I can’t just cook it until it reaches 155 degrees.
How long should I cook it and at what temperature?

Using a meat thermometer?

I'm planning to cook a pork tenderloin for dinner tomorrow. I'll be using a meat thermometer (non digital) to confirm that the tenderloin is fully cooked. I've never used one before and I have a some questions.
What internal temperature should pork tenderloin be cooked to? Do I insert the thermometer at the beginning or end [...]