Lesson 2.4

In lesson 2.4 there is a sentence I don't quite understand. 
The lesson says that the word 系, jì, means fasten, but in the sentence

qǐng dàjiā jìhǎo ānquándài, 

there is a hǎo after the jì. Why is it so? And is the pinyin for 系 really jì? In some places I see the pinyin xì for the word. 
Could someone help me to understand this?

According to ' Yabla player ' it is both and is used many more ways as well
系
xì
system
department
faculty

系 [Traditional 係]
xì
to connect
to relate to
to tie up
to bind
to be (literary)

系 [Traditional 繫]
jì
to tie
to fasten
to button up

系 [Traditional 繫]
xì
to connect
to arrest
to worry

I think 系好 (xì hǎo) is an example of a two syllable Chinese word which means "to fasten". I found that in order to see this word in Google Translate using a Hanzi input method, I had to type xihao, not jihao. This seems to be an alternate Pinyin representation.

Okay, thank you for your answers! 

你们好！

You are correct in your analysis of this word, though I will add a little more explanation here.

系 (jì) does indeed mean 'to tie' or 'to fasten', and 好(hǎo) in this context is actually a complement that means an action is completed or done to its fullest extent. Therefore, 系好安全带(jìhǎo ānquándài) - doesn't just mean 'buckle your seatbelt', but more 'fasten your seatbelt securely'.

I hope this helps and let me know if it needs anymore explanation.

   -   Lin Ping

Thank you for the clarification. It looks like 好(hǎo) has many uses.