Hello! can you help explain why these are the answer choices? Thank you!

[Questions 78] The demand for fresh strawberries is q = 200 5p and the supply is q = 60 + 2p. 4. What is the equilibrium price? A. $10 B. $20 *** C. $40 D. $50 E. [Noneoftheabove] 5. What is the price elasticity of demand at the equilibrium price? A. -5 B. -2 c. -1 *** o. -/2 6. A monopolist faces the inverse demand curve p = 64 2q. At what level of output is his total revenue maximized? A. 24 B. 8 C. 32 D. 16 ***