Answer:

1) happen --> happened

2) arrive --> arrived

3) take --> took

4) stay --> stayed

In the opening of the question, there is a line that says, "She is in San Francisco right now". But don't let that line fool you into thinking that you're going to put it into the present tenses. As she is writing right now, the letter is written in the past (after being sent to Rina), so that is why you have to use past tense.

Hope this helps, sorry if the answer is wrong. If the answer is correct, please give this answer a "Brainliest Title".

Thanks!