Hey there!
Functions are basically like machines you put a number into and they give you a new one as an output. This f represents this machine. f(x) represents whatever the output is because it is the x after it has gone through the function machine.
We want to figure out what x is when f(x)=12. Well, we can simply replace f(x) with 12 in the first equation and solve for x!
12=-16x+8
We flip the equation so x is on the left side.
-16x+8=12
We subtract 8 from both sides.
-16x=4
We divide both sides by -16.
x=-1/4
Have a wonderful day! :D
