#### Answer

$12$

#### Work Step by Step

RECALL:
$f(a)$ represents the value of the function $f$ when $x=a$.
Thus, $f(-1)$ represents the value of the function $f$ when $x=-1$.
Substitute $-1$ to $x$ in the function $f$ to obtain:
$f(-1) = (-1)^2-5(-1)+6
\\f(-1)=1-(-5)+6
\\f(-1)=1+5+6
\\f(-1)=12$