Random Samples of Monthly Rent Prices, in Dollars, for Studio $\mu_\mathrm{H}-\mu_\mathrm{p}$

Short Answer

Random samples of monthly rent prices, in dollars, for studio and one-bedroom apartments, were obtained for the Pennsylvania cities of Harrisburg and Philadelphia in July 2007. A 90% confidence interval for the difference in population means $\mu_\mathrm{H}-\mu_\mathrm{p}$ turns out to be (-$261.1, -$22.3).
-Determine the midpoint of this interval.