Answer
$b=8, -8, 16, -16$
Work Step by Step
Step 1. Given $x^2+bx+15$, the last term $15$ can be the product of the following two numbers: $3\times5, (-3)\times(-5), 1\times15, (-1)\times(-15)$
Step 2. The value of $b$ is the sum of the two numbers; thus we have $b=8, -8, 16, -16$ as possible values.
