The equation for a line is this:
y = mx + b,
where "m" is the slope (rate of change, or the ratio of the rise and the run) and "b" is the y-intercept (the point where the line passes through the y-axis).
In a vertical line, b would be equal to zero; and the line would pass through the x-axis instead.
So, in this particular case, the equation would be this:
y = 0x + 3 = 3
The answers to this question are 3 and 0.