3. Use a graphing utility to determine the absolute or relative extrema of the function \( f(x)=x^{4}+3 x^{3}-4 x \) Round answers to three decimal places.
Problems 5-9, evaluate each function and interpr
5. The \( \operatorname{cost} C \), in dollars, to produce \( x \) units of a ne is given by the function \( C(x)=85 x+150 \) for \( x \)
A. Find \( C(20) \) and interpret the meaning.