price-demand equation provided,express price, interpret marginal cost function, marginal revenue, marginal profit

A. Price p in terms of demand, x:
So,
B. Marginal cost,
C. Total revenue, TR = price*quantity
So,
So, Marginal revenue, MR(x) = 
MR(x) = 10 + 0.002*x
So, for x = 2000,
Now, for x = 5000,
So, for x = 7000,
The marginal revenue is higher for x = 7,000 whereas it is minimum for x =...