round 90 to the nearest ten
372 rounded to the nearest hundred is 400
300
45 + 39 = 84, so if you want to round to the nearest ten, that's 80, or nearest hundred is 100. Otherwise, it doesn't turn out to a decimal, so it doesn't need rounding to the nearest one.
100 100
100
100
10100
4198 to the nearest 100 = 4200
500
7675 rounded to the nearest 100 is 7700.
The answer is zero.