Need help differentiating a problem

Question

I attempted to differentiate: $$-kx^3+3k$$

And using power and constant rule I got: $$-3kx^2 + 3$$

The answer turned out to be the above without the $+3$.

Can someone help me point out where I went wrong? Thanks

Answer 1

Remember, $k$ is a constant, not a variable. You are differentiating with respect to $x$. So $3k$ is also a constant, thus the derivative of $3k$ is $0$.

Answer 2

Note: $3k$ is a constant when differentiating in terms of $x$.

$3k=3k\cdot x^0$