Answer:
parallel
Explanation:
The "work" is to recognize that both equations describe horizontal lines. All horizontal lines on the Cartesian coordinate grid are parallel.
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Additional comment
y = constant . . . . . a horizontal line (y=0 is the x-axis)
x = constant . . . . . a vertical line (x=0 is the y-axis)
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If you wanted to go to the trouble, you could compare the equation ...
y = constant
to the slope-intercept form ...
y = mx +b
Your comparison would note that m=0. That is, the slope is zero, so the line is horizontal. All lines with the same (zero) slope are parallel.