Dividing a 90-day stay in the US under the VWP

I am currently visiting Hawaii for an extended period, and will be flying to Australia for a week during my stay in the US. Here's my itinerary:
- Day 0: Enter US
- Day 45: Fly to Australia
- Day 52: Re-enter the US
How many days am I able to stay once returning to the US if the 90-day counter is not reset? Would it be an additional 45 days (i.e. first 45 days + second 45 days --> 90 days in total, not including Australia trip), or an additional 38 days (i.e. first 45 days + 7 days out of the country + 38 days --> 90 days in total)?
Note: This is not a visa run trip, I don't need the 90-day counter to be reset, but I wanted to check if the 90 day period can be divided as per the itinerary described above.
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What is the Visa Waiver Program in USA | ESTA | Stay for 90 Days in the U.S.A | Zavala Texas Law
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