Lets play this game.

I and my Friend was working as a spy, we are going to a military base to spy and get some information. We have dressed as a soldier and on getting there
we realize that the entrance was heavily guarded.
Every soldier who wanted to enter will answer a code number. If he got it wrong, he will be killed.
We have to study them.

As we were lookinq.
A soldier came, the soldier who were at the entrance said 12, he reply with 6.
Another came, the soldier said 1
and he replied with 3. He entered.

Another sets of two soldier came.
The soldier said 5 and one of them replied 4. The soldier said 9 and the 2nd soldier said 4.

Now my friend go and the soldier said 6, he replied 1, he was killed.

Now its my turn,
he said 4, what should i reply him??

4. There are 4 letters in four, 3 in one, 6 in twelve, 4 in nine. Only that 5 looks somehow. Sure about that part?

4