What is the definition of f(x)?
and where on the graph can you find it?

F(x) is just another way to express the "y" in an equation.  f(x) is function notation.  f(x) = 3x-4 is just another way of writing y = 3x-4.  f(x) is found on a graph as the y value that comes out when the x value is applied to the function.

9/12 is the answer because 3/4 times 3 each is 9/12