Question

What is the slope and y-intercept of the line y=-7?

Answer 1

Slope is zero;
Y-intercept at `x=0, y=-7`

Explanation:

Your line is perfectly horizontal; so it is neither going up (positive slope) nor down (negative slope)having a slope equal to zero.
It crosses the y axis at `x=0, y=-7` and never crosses the x axis.
Graphically:
graph{0x-7 [-20.27, 20.28, -10.14, 10.13]}