PT75.S1.Q19 - economist: although average hourly wages

https://classic.7sage.com/lsat_explanations/lsat-75-section-1-question-19

Hi everyone! I am really confused on this question.. I understand how the correct answer (B) explains why the average in the country as a whole went down, but I don't understand how it explains how the average in each region went up.

Any help would be awesome!

Thank you!