The first 8 (reading from L to R).
millions
6 is in hundred millions place.
7 is in hundred millions place.
7
The 4.
To write 309,099,990, you would start with the digit 3 in the hundred millions place, followed by 0 in the ten millions place, 9 in the millions place, a comma to separate the millions and hundred thousands places, then 9 in the hundred thousands place, 9 in the ten thousands place, 9 in the thousands place, another comma to separate the thousands and hundreds places, 9 in the hundreds place, 9 in the tens place, and 0 in the ones place.
5,763,666,666,696
To round 925,913 to the millions place, you look at the hundred-thousands place, which is 9. Since it is 5 or greater, you round up. Therefore, 925,913 rounded to the millions place is 1,000,000.
The millions, then the Ten Millions, then the Hundred Millions, then the Billions, the Ten Billions, the Hundred Billions, the Trillions, the Ten Trillions, the Hundred trillions, the Quadrillions, the Ten Quadrillions, the Hundred Quadrillions, the Quintillions and so on.
1,000,000,000
498,765,321
This would be a lot easier if one of the numbers was underlined. From right to left, this number has 0 in the ones place, 3 in the tens place, 1 in the hundreds place, 5 in the thousands place, 7 in the ten thousands place, 2 in the hundred thousands place, 6 in the millions place, 1 in the ten millions place and 4 in the hundred millions place.