Answer:
correct answer is b. less than $10
Step-by-step explanation:
solution
latest vampire novel = $10
and here Equilibrium price meaning that here is balance 
and equilibrium between supply of good and demand for that same goods
so demand and supply is balancing each other
and if there too much supply then price will go down and demand will rise up
but here he reduced price and their demand go up 
so correct answer is b. less than $10