Hello!
First of all, we need to find the slope of our line. To do so we divide the difference in the y-values by the difference in the x-values as shown below.
=-1
Therefore, our slope is -1.
Now we plug our slope and a point from our line (1,2) into the slope intercept equation and solve for b.
2=-1(1)+b
2=-1+b
b=3
Now we have our final equation below.
y=-x+3
I hope this helps!