Answer
$4i,-\frac{2}{3},\pm\sqrt {11}$
Work Step by Step
Step 1. Given a zero $x=-4i$, we know another zero is $x=4i$, thus $(x+4i)(x-4i)=x^2+16$ is a factor.
Step 2. Perform a division as shown in the figure to get the quotient $3x^3+2x^2-33x-22$ (one can also perform synthetic divisions to get the same result).
Step 3. Solve $3x^3+2x^2-33x-22=0$ graphically and use synthetic division to find a zero $x=-\frac{2}{3}$ and a new quotient $3x^2-33$
Step 4. Solve $3x^2-33=0$ to get $x=\pm\sqrt {11}$
