Answer
$\{-5,-3,3 \}$
Work Step by Step
Step 1. List possible rational zeros as $\pm1,\pm3,\pm5,\pm9,\pm15,\pm45$
Step 2. Use synthetic division to find a zero as $x=3$ as shown in the figure.
Step 3. Use the quotient and solve $x^2+8x+15=0$ or $(x+5)(x+3)=0$ to get $x=-5, -3$
Step 4. Thus we have the solution set $\{-5,-3,3 \}$
