X: I hope you have a enjoyable stay. / O: I hope you have an enjoyable stay.
X: My husband had a MRI. / O: My husband had an MRI.
X: Sometimes it is difficult to live a honest life. / O: Sometimes it is difficult to live an honest life.
"An" comes before vowel SOUNDS. It does not matter how the words are actually spelled. Further reference can be seen here: A vs. An Explanation
