What pattern exists in the three places in each period? 356,039

I don't understand this

also
Use number names and numerals to write 900,000+60,000+3,000+100+4

Step-by-step explanation:

a) Each place in our decimal place-value number system has a name. In the number 356,039, the left-most digit 3 is in the hundred-thousands place, so it is read (by itself) as "three hundred thousand." Together, the digits 356 of that number signify three hundred fifty-six thousand. They are said to be in the "thousands period." Each period of three digits will be grouped like that to specify the number of hundreds, tens, and ones in the period.

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b) The given expanded form adds up to give ...

  963,104

Based on the above discussion, the name of this number is ...

  "nine hundred sixty-three thousand one hundred four"

Using digits to help write this, it would be 963 thousand 104.