Verified answer

you need to think of the equation

y = mx + b where "m" is the slope of the line and "b" is the y-intercept (the point where the line crosses through the y axis i.e. where x=0)

given that the slope is zero, this means that it is a flat line (think of slope as rise/run and because it is zero the slope is 0/(any number)

meaning that there is zero "rise" and the line is flat.)

that said, just draw a horizontal line through the point (5,-1) and you should get your y-intercept or "b" value.