Math

 I have a homework 

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)=12000, and f′(30)=−450. (What does this mean?) 

R′(30)=?

R′(30)=