199
The mystery number is 155. When rounded to the nearest hundred, it rounds to 200. The sum of its digits is 1+5+5=11 which is greater than 10, so we must adjust the digit in the hundreds place. When rounded to the nearest ten, 155 rounds to 160, which has digits summing up to 1+6+0=7.
To round to the nearest hundred and ten both being 200 it leaves 9 possibilities. 195,196,197,198,199,201,202,203, and 204. The only one with digits adding up to 19 is 199.
7200
7550 is the smallest number than rounds to 7600 when rounded to the nearest hundred.
The lowest number that rounds to 700 to the nearest hundred would be 650.
The number 370.14 rounds up to 400 to the nearest hundred.
8600
199 If it's 200 rounded to nearest ten, then the number must be between 195 and 205. Only 199 has the correct digit sum.
Half of 100 is 50, so the smallest number that rounds to 400 to the the nearest hundred is 400 - 50 = 350.
3200
Anything from 755 to 764