What is the maximum number of relative extrema a polynomial function can have?

Relative extrema occur where the derivative is zero (at least for your polynomial function). So taking the derivative we get

20x3−3x2+6=0

This is a 3rd degree equation, now if we are working with complex numbers this equation is guaranteed to have 3 solutions by the fundamental theorem of algebra. But the number of real roots are 1 which can be found out by using Descartes' rule of signs. So the maximum number of relative extrema are 1.

Im sorry but what on

21, i'm pretty sure it's right lol