question help 4.7 from textbook

I cannot seem to get a graph to plot. the picture of the code is supposedly correct. Im supposed to type in >>plot(Poly(3,2,1),-3,3) but get an error saying i need to convert the poly to double. im honestly not sure what im doing wrong. The question comes from programming and engineering coomputing with matlab 2018 textbook problem 4.7. ive attached the question and the "correct code" . please help!

[Walter Roberson]

Please show the exact error message.

What shows up for

which Poly