what is the calculation here?

55. Fixed costs are 700,000 per year and a variable cost of 70 is incurred for every additional unit produced. The current selling price is 150 and at this price 10,000 units are demanded per year. It is estimated that for each successive increase (decrease) in price of 2, annual demand would be proportionally reduced (increased) by 500 units. What is the marginal revenue? A) 70-0.001x B) 190-0.008x C) 250-0.002x D) 150-0.004x