Posted: Tue Aug 16, 2016 2:22 am
six-figure (note the hyphen) is given in dictionaries as an adjective used only before a noun e.g. a six-figure salary (the adjectival nature of the unit there is evident in basic substitutions such as decent or handsome but not e.g. *handsomely). In your first example meanwhile the yes, noun (well, noun phrase) is rather just six figures (note the lack of the hyphen, and now the plural -s ending), with the six a form of determiner (or if you prefer, just a number). The addition of the prepositions in your second and third examples merely serves to put the pay in the stated bracket or range (not that that wasn't deducible from the first example LOL).
You've been asking these questions for years now, so again I would respectfully suggest that you read up a bit more on grammar and syntax. The chapter on 'English Word Classes and Phrases' in The Handbook of English Linguistics (ed. Bas Aarts) might be a good place to start (you can no doubt find a free version online somewhere), but for a carefully-written and internally very consistent grammar (dry and sometimes demanding though it is) I suggest knuckling down to Huddleston & Pullum's A Student's Introduction to English Grammar, which will help if and when referring to its parent work, the desk-thumping CGEL, or similar.
Note however is that no grammar will ever contain or discuss every last item you might come across (e.g. what exactly may follow the verb PAY?), but the more you "pay your dues" with such reading, the less you should find every little thing too perplexing, allowing the focus to shift to wider issues or true essentials. One thing you will have to get better at is fudging a bit sometimes and feeling your way towards real-world functional generalizations (e.g. that guff I wrote above about putting the pay into a thus "more explicit" bracket. Is the prepositional phrase an adverbial, or an adjunct, or...even a prepositional phrase? The answer is, does it matter, as it is at most merely implicit than explicitly stated in certainly the first example).
But I appreciate that actual communication may be a quite distant concern to some "testing" types, and that they may take issue with whatever answers no matter how helpful the answer may be from at least a communicative standpoint (K.I.S.S, WYSIWYG, etc). Worst-case scenario however is that the people (Chinese teachers of English?) asking you these questions know full well the answers and are having fun seeing if (that) you do(n't). So, again, I really think you should do some (or some more!) reading. Mind if I ask what books or resources you have read or usually refer to?