Answer:
blue line : y = 3
black horizontal line : y = 0
black vertical line : x = 0
Explanation:
it is really simple.
blue line : no matter what value we pick for x, the functional value for y is always 3. and that defines the equation y = 3 + 0*x or simply y = 3.
the same with the black horizontal line. the difference is that y is now always 0. so, y = 0.