Step-by-step explanation:
First we take three of the chains and place next to each other in the form of a triangle.
Now we take the fourth chain. open each link of the fourth chain.
For opening each link of fourth chain it costs 2+2+2= 6 cents.
Now connect each opened link with the vertices of the triangle to connect all the 3 chains.
Close the vertices of the triangle to make necklace.
For closing it costs 3+3+3= 9 cents
Total cents = 6+9= 15 cents