Help me find what's wrong and fix it? [Algebra 1]

Hi!
I have to figure out what they did incorrectly in the textbook and then explain what they did wrong. I just got confused, so I need some help.

(-5z)(-8)(z) = (-8)(-5z)(z)
=(-8)(-5)(z)(z)
=40(z ⋄ z)
=-40z²

the answer should be positive 40z^2 not negative

Its supposed to be positive 40z^2 (squared).

The second step: -8 * -5 = +40

...which you seem to have done in the third step. But then you added the negative sign for some reason for the last step.

40z²