c$.$ Note that we haven't given you the original market price of simple bicycles$-$why don't you need to know it$?($Hint: The answer is a mix of geometry and economics.$)$

It's unnecessary because the

equilibrium price can be calculated from the graph. Since the price$-$controlled quantity is one$-$half of the equilibrium quantity, we can infer that the consumers' price at the price$-$controlled quantity, $$80,$ is one$-$half of the equilibrium price, which is then $$40.$

calculations require the quantity supplied at the controlled price, the price consumers are willing to pay and the price producers are willing to accept for that quantity supplied, and the equilibrium quantity, but not the equilibrium price. equilibrium price is the average of the consumers' willingness to pay and the producers' willingness to accept values at the price$-$controlled quantity: the average of $$80$ and $$30$ is $$55.$