That rounds to zero.
21 rounded to the nearest hundred is zero. -- The even hundred above 21 is 100. -- The even hundred below 21 is zero. -- 21 is closer to the lower one than it is to the higher one.
When rounding 21 to the nearest hundred, we look at the digit in the tens place, which is 2. Since 2 is less than 5, we round down to the nearest hundred, which is 0. Therefore, 21 rounded to the nearest hundred is 0.
21 to the nearest tenths is 21.0
20.663 to nearest whole number is 21
700
100
That is 4800
4198 to the nearest 100 = 4200
100
100
100