Answer:
Explanation:
f(x) = x^2 + 4x is specified as a function. When the x is replaced in "f(x)" is replaced with a number, you treat it as a variable.
In this case, f(-3) is almost exactly like saying x = -3.
Everywhere x is in the function is replaced with -3, because you are plugging it in to find a value. Here is a demonstration:
f(-3) = (-3)^2 + 4(-3)
f(-3) = 9 - 12
f(-3) = -3
The answer to your question is -3. Don't be afraid to ask anymore questions regarding this if you are confused.