What is the outlier of these numbers? 42,38,45,68,40,39,39,41

It should be 68 because it's the biggest number there

My definition of an outlier is a number that is abnormal or the most different on a data set.

Sometimes it can be easy to know if a number is too high or too low in a data set.

In your data set, I would say the outlier is number 68 because it's the highest.