Pricing

Sir i have a problem with BPP Kit mcq
Q;A company is selling a product at a price of $120/U.At this price it sell 200000 units per period.IT has been estimated that for every $5 increase/reduce in price,sales demand will fall/increase by 10000 units

I am able to find “a=220” and “b=.0005″

But in your lectures you said MC is given in question as variable cost..But not in this Question
So how we find ”’Selling price for maximised total sale revenue”??

Many thanks