According to math-quiz.co.uk the $x^3+12x^2−19x=−20$ factorised is $(x−4)(x+5)(x+1)$ My answer in red under "Your answer" isn't my answer I just had to chose something since it was a multiple choice

My working to check if it's correct

$(x−4)(x+5)(x+1)$

$(x^2-4x+5x-20)(x+1)$

$x^3+x^2-4x^2-4x+5x^2+5x-20x-20$

$x^3+2x^2-19x-20$

Am I wrong or is math-quiz.co.uk wrong?
The given expression has a real root $\approx  -13.5153$ and two complex roots.

The question was set cleverly to start with, but the setter seems somehow upset.
Edit=I hadn't checked your answer, I just saw their answer is wrong.

Maths quiz is wrong, but your answer is wrong too. The real answer is a lot more complicated, and includes a factor with no real solutions. 

Your proof that their answer is wrong is correct though.