The slope of the equation in the picture

Y - 3 = 0
y = 3

learn this : (it really does help)
HOY -- horizontal line, 0 slope, represented by y = a number.
VUX -- vertical line, undefined slope, represented by x = a number.

so if u have y = 3this is a horizontal line with a 0 slope <==

** if it would have been x = 3, then u would have had a vertical line with an undefined slope