I don't understand how the derivative of

$\displaystyle R(x)=\frac{1}{10000}(60000x-x^2)$

is

$\displaystyle R'(x)=\frac{1}{5000}(30000-x)$

I tried it with both the quotient rule and the product rule and I didn't get the same answer. Because isn't the derivative of a constant always 0?

Please and thank you