The figure below shows $f(x)$ and its local linearization at $x=a$, $y = 4 x - 4$. (The local linearization is shown in blue.)

What is the value of $a$?
$a =$

What is the value of $f(a)$?
$f(a) =$

Use the linearization to approximate the value of $f(3.2)$.
$f(3.2) =$

Is the approximation an under- or overestimate?
(Enter under or over.)