Answer
$\frac{3ln7}{1-ln7}\approx- 6.172$
Work Step by Step
1. $7^{x+3}=e^x \Longrightarrow (x+3)ln7=x \Longrightarrow (1-ln7)x=3ln7 \Longrightarrow x=\frac{3ln7}{1-ln7}\approx- 6.172$
2. Check, $x=\frac{3ln7}{1-ln7}$ fit(s).
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