Question 283267
for all these f of x type problems, you are being asked to evaluate the expression at a given value of x.

So all you do is substitute in the given value of x everywhere in the given expression. The simplify and evaluate. 

Given {{{f(x)=3x^2-4x}}}
Solve for f(0).
So sub in x=0 everywhere in the expression
{{{f(0) = 3*0^2-4*0}}}
{{{f(0) = 0 - 0}}}
{{{f(0) = 0}}}

If they then asked, what is f(2). do the same process
Given {{{f(x)=3x^2-4x}}}
Solve for f(2).
So sub in x=2 everywhere in the expression
{{{f(2) = 3*2^2-4*2}}}
{{{f(2) = 3*4 - 8}}}
{{{f(2) = 12 - 8}}}
{{{f(2) = 4}}}

make sense?
If yuou do that for a bunch of values for x, you get a bunch of points. Plot thos points and connect the dots to get a graph of the expression (a function in this case)

here is a graph
{{{graph(400,400,-10,10,-10,10,3x^2-4x)}}}