Answer
The first step was wrong.
The correct answer is $f(-24)=-88$.
Work Step by Step
The given function is $f(x)=4x+8$.
Substitute $x=-24$.
$f(-24)=4(-24)+8$ This step is done wrongly by JT.
Clear the parentheses.
$f(-24)=-96+8$
Simplify.
$f(-24)=-88$.
