A manufacturer produces bolts of a fabric with a fixed width. A quantity $q$ of this fabric (measured in yards) that is sold is a function of the selling price $p$ (in dollars per yard), so we can write $q=f(p)$. Then, the total revenue earned with selling price $p$ is $R(p)=pf(p)$.

Find $R'(30)$, given $f(30)=10000$, and $f'(30)= -450$. (What does this mean?)

$R'(30) =$