The function f is defined by f x = 80 - 6 x . What is

Choice B is correct. It’s given that function $f$ is defined by $f\left(x\right)=80-6x$. The value of $f\left(7\right)$ can be found by substituting $7$ for $x$ in the given function, which yields $f\left(7\right)=80-6\left(7\right)$, or $f\left(7\right)=80-42$, which is equivalent to $f\left(7\right)=38$. Therefore, the value of $f\left(7\right)$ is $38$.

Choice A is incorrect. This is the value of $80-67$, not $80-6\left(7\right)$.

Choice C is incorrect. This is the value of $80-6\left(1\right)$, not $80-6\left(7\right)$.

Choice D is incorrect. This is the value of $80-6+7$, not $80-6\left(7\right)$.