Since this is a lot, I'll help with the first 6 odds.
1) 6, the place after 8, is over the halfway point, 5, so the number rounds up to 9,000,000.
3) 1, the place after 1, is under 5, so the number rounds down to 803,100.
5) 4<5, rounds down, 2,000,000,000.
7) The first 9 is the billion's place, and the place after that is >5, so rounds up, 10,000,000,000.
9) 4 is in ten-thousands, 7>5, rounds up, 350,000.
11) 2nd 9 in thousands, 1<5, rounds down, 1,399,000