I need help understanding this. I am having a hard time. A detailed explanation would be great appreciated. Thank you

Sarahhas been selling 5,000 baseball caps per quarter at $7.50 each. When she decreased the price to $4.50, the total sales reached 6,500 baseball hats.

a.What is the demand elasticity? Show calculations.

b.If Sarah's marginal cost (MC) is $4 per cap, what would the desired markup be and what is the initial (actual) markup?

c.Was decreasing the price profitable for Sarah's baseball caps business? Explain.