Let $f(x) =3^{-x}-5$ and $g(x)=-x^3-4x^2+x+6$.
The graphs of $y=f(x)$ and $y=g(x)$ are shown below. The point $(a,b)$ is on the graph of functions $f$ and $g$.
**The value $x=a$ is a solution to which of the following equations?**
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