Rejection with mean and standard dev given

So I am having a little brain fart. The problem reads,

The snack pack of potato chips is advertised to weigh 3.5oz . The weights are normally distributed with a mean of 3.5oz. And a standard deviation of.2 oz. an inspector rejects packs that weigh less than 3 oz and more than 4 oz. what is the probability that a randomly selected pack will be rejected?

This is off of a test. I got it wrong and the teacher never went over how to get the right answer just showed us what it was. Help please!! Thank you for your time.