Q. Pure pool services provide weekly pool maintenance in Beverly Hills. Dozens of firms provide this service. The service is typically sold as a four-month contract. The market cost of a fourth-month contract is $115. Pure has fixed cost of $3500 for the summer. The manger of pure has estimated the following marginal cost function, using data from the last two years. MC=125-0.42Q+0.0021Q^2, where MC is measured in dollars as well as Q is the number of pool serviced each summer. Each of the estimated coefficients statistically significant at the 95 per cent confidence interval. What is the optimal output level?