Find $x$ where $x$ is the least non-negative residue such that
$$ x \equiv 8 × 9 × 10 × 11 × 16×17 × 18 × 19 \pmod {13} $$
We start as follows
$$ \begin{align} x & \equiv 8 \times 9 \times 10 \times 11 \times 16 \times 17 \times 18 \times 19 \pmod {13} \\ \\ & \equiv (-5) \times (-4) \times (-3) \times (-2) \times 3 \times 4 \times 5 \times 6 \pmod {13} \\ \\ & \equiv (-5) \times (-1) \times (-2) \times (-1) \times 5 \times 6 \pmod {13} \quad \quad \text{ using } 3 \times 4 \equiv -1 \\ \\ & \equiv (-2) \times 6 \pmod {13} \quad \quad \text{ using } (-5) \times 5 \equiv 1 \\ \\ & \equiv -12 \pmod {13}\\ \\ & \equiv 1 \pmod {13} \end{align} $$
So the least non-negative residue is $x=1$.