300
279 rounded to the nearest hundred is 300. When rounding, you look at the digit in the tens place, which is 7 in this case. Since 7 is 5 or greater, you round up to the next hundred.
300
853 rounded to the nearest 100: 900. 10853 rounded to the nearest 100: 10900.
40,000,000
100
100
0
555 rounded to the nearest 100 is 600.
97 rounded to the nearest hundred is 100. 97 rounded to the nearest ten is 100
100
100
100