Hello, could somebody please help me please.

Find the coordinates of points where the graph f(x) has horizontal tangents. As a check, graph f(x) and see whether the points you find look as though they have horizontal tangents

F(x)= 1/3x^3-3x^2-16x+8

my answer is

f(x)=-141.3

f(x)=25.3

is that correct?

thanks