Well, first, the equation that you are looking for is Y = MX + B. To find B, look at the first dot on the Y-axis. It starts at positive 3, so, you know your equation will end with +3. Next, to find MX, start at the either dot, and find the Rise/Run. In this particular equation, the rise is 1, and, the run is -2, because it's going backwards (negative line). Meaning, the line's equation would be, f( x )= -1/2x + 3.
