Answer:
each circle weight 3 grams 
Explanation:
I think your question missed key information, allow me to add in and hope it will fit the orginal one. Please have a look at the attached photo, 
This hanger is in balance. There are two labeled weights of 8 grams and 20 grams.The four circles each have the same weight.
what is the weight of each circle.
My answer: 
Let x is the the weight of the circle 
Because this hanger is in balance, so we can form the equation: 
20 = 8 + 4x
<=> 4x = 20-8 
<=> 4x = 12 
<=> x = 3
So each circle weight 3 grams