Answer
$11$, see explanations.
Work Step by Step
Step 1. Based on the Remainder Theorem, $f(-6)$ is the remainder when performing a division of $f(x)$ by $x+6$.
Step 2. Perform a synthetic division as shown in the figure; we can get the remainder as $f(-6)=11$.
Step 3. It can be seen that we can obtain $f(-6)$ easily using the Remainder Theorem and with division instead of evaluating $f(-6)$ directly.
