Can show me how to get this answer?

What you are given is f(x)=4x-8. When it says f(16)-f(0), it is telling you what the values of x should be equal to when placed into the given function. Whenever you see an x in your given function, it should be replaced with the number in parentheses after x. In this case, what you want to know is x=16 and x=0 since these are the numbers following f.
To get to your answer of 64, start out by setting up your equations.
Your first would be 4(16)-8 (since you’re filling 16 in for x).
Your next would be 4(0)-8 (since you’re filling 0 in for x).
Then you want to subtract these 2 equations from one another, as that’s what it’s asking for in the problem AKA f(16)-f(0).
4•16=64. 64-8= 56.
4•0=0. 0-8= -8.
56-(-8)= 64 since 2 negatives equal a positive.
Hope this helped! Please message me if you want to see the problem done out on a piece of paper or if you have any more questions!