The 3 chickens amount to $3 x 3 = $<<3*3=9>>9.

Hence, the potatoes cost $15 - $9 = $<<15-9=6>>6.

# Answer

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<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Mrs. Thompson bought 3 chickens for $3 each. She also bought a bag of potatoes. Mrs. Thompson paid $15 in total. How much did the potatoes cost?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
6
Mrs. Thompson bought 3 chickens for $3 each. She also bought a bag of potatoes. Mrs. Thompson paid $15 in total. How much did the potatoes cost?
train