Refer to the figure below for this question. Class C airspace surrounds moderately busy airports. ATC provides radar service for IFR and VFR traffic. Two-way communication and altitude-reporting transponders are required within the 5-nm-radius core and the 10-nm radius shelf. Not depicted on charts is the Class C outer area, which extends from 10 nm from the airport to (______ nm, and two-way communications are (_____).


20, voluntary


20, mandatory


30, voluntary


30, mandatory

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