Question 162766
if f(x) = x, then
f(3) = 3
f(5) = 5
you substitute the x with a value of x and solve.
in your problem,
f(x) = 3*|x|
set y = f(x) so the equation becomes y = 3*|x|.
now pick some x values and you'll get some y values.
example:
if x = 3, f(x) = y = 3 * |3| = 3 * (3) = 9
if x = 1, f(x) = y = 3 * |1| = 3 * (1) = 1
if x = 0, f(x) = y = 3 * |0| = 3 * (0) = 0
if x = -1, f(x) = y = 3 * |-1| = 3 * (1) = 1
if x = -3, f(x) = y = 3 * |-3| = 3 * (3) = 9
-----
whether x is negative or positive, the y value which is the same as f(x) will always be positive.
-----
plot points from x = -5 to x = + 5 at least and you'll see the shape of the curve.  
you may already see it from the points already plotted here.