deciding selling price

Hi Sir, I was taking this revision mock F5 exam and was not able to get answer for this. Can you please help me how to do this? At a selling price of $200, the demand will be 100,000 units per annum. The demand will change by 10,000 units for every $30 change in the selling price. The fixed cost are $60,000 per annum, and the variable costs $8 per unit. At what selling price per unit will the profit be maximised?