Answer
See below
Work Step by Step
Given: $x^4+x^3-15x^2-8x+6=-45$
Separate the left side and the right side of the equation:
$y=-45\\y=x^4+x^3-15x^2-8x+6$
The red graph is the graph of $y=-45$. The blue graph is the graph of $y=x^4+x^3-15x^2-8x+6$