Concept:
Time taken to complete work is inversely proportional to efficiency.
If the ratio of days taken by A, B, and C is:
\[
3:4:6
\]
then let their times be:
\[
3x,\;4x,\;6x
\]
To find the exact number of days for B and C together, we first need the value of \(x\).
Step 1: Checking Statement (I).
Given:
A is \(100\%\) more efficient than C.
This means:
\[
E_A=2E_C
\]
Since time is inversely proportional to efficiency:
\[
T_A=\frac{T_C}{2}
\]
This only confirms:
\[
3x=\frac{6x}{2}
\]
which is already consistent with the given ratio.
No actual value of \(x\) is obtained.
So, Statement (I) alone is not sufficient.
Step 2: Checking Statement (II).
Given:
C requires 27 days more than A.
From ratio:
\[
T_C-T_A=27
\]
\[
6x-3x=27
\]
\[
3x=27
\]
\[
x=9
\]
Thus,
\[
T_B=4x=36
\]
\[
T_C=6x=54
\]
Now combined work rate:
\[
\frac{1}{36}+\frac{1}{54}
\]
Taking LCM \(108\):
\[
=\frac{3+2}{108}
\]
\[
=\frac{5}{108}
\]
So total time:
\[
=\frac{108}{5}
\]
\[
=21.6 \text{ days}
\]
Thus, Statement (II) alone is sufficient.
Hence, the correct answer is (B).