Please I don't understand please

For the first part, you are choosing either "when" or "while" to replace each blank for each problem.

"When" is used to signify either an interruption or actions with chronological order (sequence). For example, the first sentence (#1) would be when because "suddenly" shows that there's an interruption in the current action, which is reading. #6 is also when because the word "then" shows that there is some type of order in the sentence (1. Angela gets home and #2. She was making coffee).

On the other hand, "while" is used to talk about actions that are happening at the same time. For example, #2 would be while because Rosie cooking dinner and her husband going to work is happening at the same time.

The second part is just changing the tense of the verb based on the sentence.

what is margin again? i’m confusion