Two sequences $x_n$ and $y_n$ satisfy the coupled recurrence system: $x_n = 0.7x_{n-1} + 0.2y_{n-1}$ $y_n = 0.1x_{n-1} + 0.9y_{n-1}$ with $x_0 = 10$ and $y_0 = 5$. Which best describes the long-term behavior of $x_n + y_n$?