The figure below shows the graph of $f$ and the graph of its local linearization $l_a(x) = 4 x - 1$ at $a$. (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 $f(2.5)$.
$f(2.5) \approx l_a(2.5) =$

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