This Instructional Activity is a part of the Lesson 12, Unit 4, Grade 8. An equation in the form of ax + by = c is called a linear equation in two variables, where a, b, and c are constants, and at least one of a and b are not zero. In this lesson, neither a nor b will be equal to zero. In the Opening Exercise, what equation did you write to represent Emily's score at the basketball game?