Another product manufactured by Delnorte Ltd is product M. At a price of $\$ 700$ for product $M$ there would be zero demand, and for every $\$ 40$ reduction in the selling price the demand would increase by 100 units. The variable cost of producing a unit of product $\mathrm{M}$ is $\$ 60$.

Delnorte Ltd knows that if the demand equation for product $M$ is represented by $p=a-b x$, where $p$ is the selling price and $x$ is the quantity demanded at price $p$, then the marginal revenue (MR) for product $M$ can be represented by MR $=a-2 b x$.

The profit-maximising output of product $M$ is:

A. 100 units 

B. 700 units 

C. 800 units 

D. 1,600 units 

E. 1,750 units