This Instructional Activity is a part of the Lesson 27, Unit 4, Grade 8. In this example, students realize that graphing a system of equations yields a solution, but the precise coordinates of the solution cannot be determined from the graph. Though the graphs of the equations were easy to sketch, it is not easy to identify the solution to the system because the intersection of the lines does not have integer coordinates. Estimate the solution based on the graph. The solution looks like it could be When we need a precise answer, we must use an alternative strategy for solving systems of linear equations. Understanding the substitution method requires an understanding of the transitive property.