You can use a formula to find the slope from the two points
m=slope
m= y_2 - y_1 / x_2-x_1
This means slope equals the change in y's for the change in x's, substitute your points into the formula to solve for the slope:
m=6-1/-1-9 --> m=5/-10 --> m= -1/2 or -0.5
Now that you know the slope, substitute the slope as well as one of the points into the equation y=mx+b (we'll use point (9,1) but either one will work ) to solve for the y-intercept
1=(9)-0.5 +b
1= -4.5 +b Add 4.5 to both sides
5.5=b
So your equation is y= -0.5x + 5.5