Rewrite the statement

$"$No good cars are cheap" in the form $"$ AAx, if $P(x)$ then $Q(x)."$ Indicate whether each of the following arguments is valid or invalid, and justify your answers.

$($a$)$ No good car is cheap.

A Rimbaud is a good car.

:$.$ A Rimbaud is not cheap.

$($b$)$ No good car is cheap.

A Simbaru is not cheap.

:$.$ A Simbaru is a good car.