Answer
a. $N=400-2(x-120)=640-2x$
b. $R =640x-2x^2$
Work Step by Step
a. Based on the given information, we have $N=400-2(x-120)=640-2x$. This gives $N=400$ when $x=120$ dollars and for every dollar increase in $x$, 2 fewer rooms are rented.
b. The revenue is given by $R=Nx=640x-2x^2$
