If you only worked in one location for your employer there should only be one entry for the line with boxes 18-20. Line 20 having the same value would indicate that all 3 lines refer to the same locality. If that is the case then you could add the lines for each box into a single line to enter into your tax return.
You should contact your employer to verify if this is true before entering a combined single entry.
This is not a problem with TurboTax as some taxpayers have wages earned in different localities while working for the same employer and each locality needs to be reported on a separate line to ensure proper credit.
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