400
478.5
400
420
15,549 to the nearest hundred
420
400
420
There are 25.4 millimetres in one inch. Therefore, rounded to two decimal places, 415 millimetres is equal to 415/25.4 = 16.34 inches.
Dividing distance travelled by speed gives 450/65 = 6.923076 recurring (that is, 6.923076923076...) hours or 415 minutes, rounded to the nearest minute.
420.
That would depend on what you were rounding it to. If rounding to the nearest whole number, then it does not need rounding. If rounding to the nearest ten, it would be 420. If rounding to the nearest hundred, it would be 400.