Write an equation for the line parallel to the x-axis through the point (0,-8)

Y = mx + c where m is the gradient (y/x) and c is the y intercept.
Plot those coordinates into the equation ; -8 = m x 0 + c.
C = -8. The line intercepts the graph at 0,-8 so it's a flat straight line as the gradient is 0.
Therefore, all you have to do is y = mx + c, where m = 0 and c = anything apart from -8

There should only be 1 solution