Slope:
The slope is found with m = (y2 - y1) / (x2 - x1).
You can use any two points, so I'd pick ones with positive x and y values.
Using (1,5) and (3,3):
m = (3 - 5) / (3 - 1) = (-2)/(2) = -1
The slope is -1.
To find the y-intercept, we can go to the point (-1,7) and use the slope of -1. A slope of -1 means that if x goes up by 1, then then y goes down by 1. So if we go from x=-1 to x=0, then the y-value of 7 will go down by 1.
y-intercept (0,6)
The equation in slope-intercept form is y = -x + 6, since we already found the slope and y-intercept.