What number, when added to the numerator and to the denominator of $\frac{5}{8}$, results in a fraction whose value is 0.4?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
What number, when added to the numerator and to the denominator of $\frac{5}{8}$, results in a fraction whose value is 0.4?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
-3
What number, when added to the numerator and to the denominator of $\frac{5}{8}$, results in a fraction whose value is 0.4?
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