Marta is making two different charms for necklace one charm has a 1 cm diameter and a 3.14 cm circumference of a similar charm has a diameter of 4 cm what is the circumference

From what I can pick up from your problem statement, you want to know "a similar charm has a diameter of 4 cm what is the circumference."  Please, would you use proper punctuation in your writing, for greater clarity:

"A similar charm has a diameter of 4 cm.  What is the circumference?"

The formula for the circumference of a circle, when the diameter is known, is 

C=d               or  C=pi*d

In this case, with diamter 4 cm, the circumference, C, is 4pi cm.