The equation for a linear line is y=mx+b. m is the slope, and b is the y- intercept(where the line hits the y axis). Slope is rise/run (rise over run). Since line D is a horizontal line, there is no rise and infinite run. This means the slope is 0/1, therefore it is 0. The y-intercept is -3. So now plug in the information to the equation. y= -3. The reason you don't see the slope or x is because any number thst you put in for x will be multiplied by zero and will equal 0. That does not have any effect on the y-intercept. Your answer is y= -3.