#### Answer

$6$

#### Work Step by Step

RECALL:
$g(a)$ represents the value of the function $g$ when $x=a$.
Thus, $f(0)$ represents the value of the function $f$ when $x=0$.
Substitute $0$ to $x$ in the function $f$ to obtain:
$f(0) = (0)^2-5(0)+6
\\f(0)=0-0+6
\\f(0)=6$