Answer:
Slope: m = 0
Equation: y = -3
Explanation:
A line perpendicular to the y-axis always has a slope of 0. Slope is calculated by (y2-y1)/(x2-x1) or rise/run or delta y/delta x (they're all the same thing, delta means difference and is notated with a triangle). When there is no change in y (perpendicular to the y-axis), no matter what the change in x is, the slope will be 0.
Since it is given that one of the points has a y-value of -3, the equation for this line would be y = -3. The formula for a linear equation is y=mx+b. Since the slope is 0, the value of mx is 0, and therefore not needed in the equation. b represents the y-intercept and in this case would be -3.