Assume that a department store was selling a brand of men's dress shirt at $100.00 per shirt. At that price, the store sold 50 shirts in one week. Next week, the store declared a "sale - buy one get one free". As a result, sale of the dress shirt incresed to 300 in that week. Based on these information, calculate the price elasticity of demand using the arc elasticity formula . What does the coefficient of elasticity indicate?

(it is my understanding that the elasticity is 2.14 but I cannot figure out how?)