Answer:
[tex]f(x) = 4x+5\\f(4)=4x+5\\f(4)=4(4)+5\\f(4)=16+5\\f(4)=21[/tex]
Step-by-step explanation:
The x in [tex]f(x)[/tex] is the number you plug into the x spot. think of f(x) like y.
[tex]f(x) =y[/tex] but it's y that tells you what x is supposed to be.
for example:
[tex]y=mx+b\\f(x)=mx+b\\f(x)=4x+5\\f(3)=4(3)+5\\f(4)=4(4)+5\\f(5)=4(5)+5[/tex]
So you can say that f(any number) is a place holder for the y that tells you what x is supposed to be plugged in.
