OG详解-OG5 数学1 Q6

The correct answer is 4. A solution to a system of equations must satisfy each equation in the system. It follows that if (x, y) is a solution to the system, the point (x, y) lies on the graph in the xy-plane of each equation in the system. According  to the graph, the point (x, y) that lies on the graph of each equation in the system is (4, 1). Therefore, the solution to the system is (4, 1). It follows that the value of x is 4.