please answer 9 and 10

***Micro Review*** 9. Calculate the price elasticity of demand for hot dogs if the price of hot dogs decreases from $4.00 to $3.50 causes the quantity of hot dogs demanded to increase from 2,000 to 2,400. (2 points - you MUST show your work) 10. The quantity of phones demanded is 40 when price is $500. When the price of the phone increases to $700, the quantity demanded decreases to 10. Calculate the elasticity of demand. (2 points - you MUST show your work)