Given that the cost of producing n watches is C(n) (unit: $), where C(n)=50000+80n
a) Find the cost of producing 60 watches.
Is the answer $54800.
b) If a shop sells these watches at a price of $1000 each,
i) Express P(n) (unit: $) to express the profit of selling n watches.
ii) Find the profit of selling 80 watches.