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The projected sales volume of a video game cartridge is given by the function s(p)=3000/2p + a where s is the number of cartridges sold, in thousands; p is the price per cartridge, in dollars; and a is a constant. If according to the projections, 100,000 cartridges are sold at $10 per cartridge, how many cartridges will be sold at $20 per cartridge?
A) 20,000
B) 50,000
C) 60,000
D) 150,000
E) 200,000
What is C.