the equation of a line in slope intercept form is y=mx+b
m=slope
b=y intercept
The first thing we can do is calculate the slope which is the change in y over the change in x or "rise over run"
2 moving up to 5 is a difference of 3
0 moving left to -3 is a -3
3/-3
we can simplify this to -1
so we know that
y=-1x+b
We still need to find the y intercept. In this case one of our points (0,2) is on the y axis. so we know that the y intercept is 2 because that is where the line crosses the y axis.
The equation then is
y=-1x+2
the coefficent for x isn't really necessary so you could write this as
y=-x+2
The graph of this line looks like this: