How is Friar John prevented from going to Mantua to deliver Friar Laurence's
letter?

Friar John cannot deliver the letter because of the plague outbreak.

Explanation:

In this Shakespeare's play, the two lovers try to find a way to be together, despite their warring families. Friar Laurence devises a plan that will help them - Romeo's girlfriend will drink a potion that will make her appear dead. Meanwhile, Romeo will receive a letter in which it is explained that she is alive, so that the two of them can escape together.

At first, everything happens as planned. However, when Friar Laurence asks Friar John to deliver the letter to Romeo, he cannot do so, because there is a plague outbreak in Mantua. Health inspectors keep him in a quarantined house.

check this quizlet it might have the answer

in june, we will have been married for eighteen months. (i am assuming this is what you want? the sentence, as you have presented it, is grammatically incorrect--   you want it corrected, yes? )