As you see in the picture, there are four 3-link chains. All you have to do is join them into a big 12-link chain. For joining two closed links, one of the links must be cut and placed onto the other link for closing.
How many minimum links will you have to cut to make the big chain ?
Refer the picture. All you have to do is cut three links from a single 3-link chain and then you can use them to join three other 3-link chains to make a big 12-link chain