Answer:
y=-3
Explanation:
The equation of a line is y=mx+c, where m is the gradient and c is the y-intercept (the point where x is 0 and y has some value).
First, we have to find the gradient and for all horizontal lines, the gradient is 0 because gradient is the rate of change in x with respect to y and y is not changing so there is no gradient since there is no change.
Anything times 0 is 0 so we can write the equation as y = c now plug in the y value and find c.
c= -3
Replace c in the equation and we get y=-3