Students write and interpret systems of two linear equations in two variables, determining whether an ordered pair satisfies both equations simultaneously and representing the solution as the intersection of their graphs. They solve systems by graphing, estimate intersection coordinates when needed, and distinguish one solution, no solution from distinct parallel lines, and infinitely many solutions from coincident lines. They model comparison and other contextual situations with systems, interpret solutions using appropriate units and meanings, and apply practical restrictions such as nonnegative or whole-number quantities.