Mention a hilly region to the west of the capital (5)

I believe the answer is:

hanoi

I'm a little stuck... Click here to teach me more about this clue!

'capital' is the definition.
(capital of Vietnam)

'mention a hilly region to the west of' is the wordplay.
'HANOI' is hidden back-to-front in amongst the letters.
But, I am unsure how the hidden word is indicated.

'the' acts as a link.

Can you help me to learn more?

(Other definitions for hanoi that I've seen before include "Asian capital on the Red River" , "Vietnamese city" , "Asian city" , "foreign city" , "Vietnamese capital" .)

I've seen this clue in the Sydney Morning Herald.

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