Mount Sinai and the Present Jerusalem

Galatians 4:25 NASB
Now this Hagar is Mount Sinai in Arabia, and corresponds to the present Jerusalem, for she is in slavery with her children.

In the first metaphor Paul used in verse 24, Hagar was the covenant that proceeded from Mount Sinai. In verse 25, Paul uses another metaphor for Hagar.
What's the second metaphor for Hagar?
Read the portion of the verse between the commas.
Who or what corresponds to the present Jerusalem?
Since Hagar is the subject of the sentence, she is the one who corresponds to the present Jerusalem.
What does "corresponds to" mean?
In the King James version, it reads "answereth to." If you were to look up "answereth" for this verse in Strong's Exhaustive Concordance, you would find that it means "to file together as soldiers in ranks." (G#4960)
What does Hagar correspond to?
Is this a comparison or a contrast?
How is the present Jerusalem of Paul's day related to the Mosaic (or Sinaitic) Covenant, represented by Hagar?
How are people who are represented by Hagar trying to achieve righteousness?
And what does Paul say about those who are like Hagar?
Is this what Paul would desire for his readers, the Galatians?
Read Galatians 1:6-8 and Galatians 3:1 and Galatians 4:1-7.