#### Answer

$2$

#### Work Step by Step

RECALL:
$f(a)$ represents the value of the function $f$ when $x=a$.
Thus, $f(4)$ represents the value of the function $f$ when $x=4$.
Substitute $4$ to $x$ in the function $f$ to obtain:
$f(4) = 4^2-5(4)+6
\\f(4)=16-20+6
\\f(4)=-4+6
\\f(4)=2$