Shen is a college student who lives in San Diego and provides math teaching for extra cash. At a wage of $25 per hour, he is willing to tutor 4 hours per week. At $40 per hour, he is willing to tutor 10 hours per week. Using the midpoint method, the elasticity of Shen's labor supply between the wages of $25 and $40 per hour is approximately_____- , which means that Shen's supply of labor over this wage range is______