To divide 343 by 9, you will use the division algorithm.
The reason is because 343 is not divisible evenly by nine.
You know this because the sum of the digits, 3+4+3 or 10, is not evenly divisible by 9.
Therefore, 343 is not evenly divisible by 9.

Radius / diameter as a length cannot be negative, that's why '-16' is wrong.