Bob is a college student who lives in New York City and teaches tennis lessons for extra cash. At a wage of $50 per hour, he is willing to teach 7 hours per week. At $65 per hour, he is willing to teach 10 hours per week. Using the midpoints formula, the elasticity of Bob's labor supply between the wages of $50 and $65 per hour is approximately , which means that Bob's supply of labor within this wage range is