A would be 30cm, B would be 29.7cm, and C would be 29.730cm.
Rounding up or down in these, a, b, c give you what to round to. in A, it wants you to round with no decimal behind the number. in B it wants you to round with only 1 decimal behind the number. and in C it wants you to round with 3 decimals behind the number.
hope this helped.
