To calculate $42^2$, Emily mentally figures the value $40^2$ and adds $164$. Emily subtracts a number from $40^2$ to calculate $38^2$. What number does she subtract?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
To calculate $42^2$, Emily mentally figures the value $40^2$ and adds $164$. Emily subtracts a number from $40^2$ to calculate $38^2$. What number does she subtract?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
156
To calculate $42^2$, Emily mentally figures the value $40^2$ and adds $164$. Emily subtracts a number from $40^2$ to calculate $38^2$. What number does she subtract?
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