you are trying to write this in y=mx+b form. m is the slope, found by taking rise over run. rise is -4-2=-6, and run is 9-1=8. so -6/8=-3/4. now plug that into the equation. y=-3/4x+b. to find b, plug in one of the points. I chose (1,2). 2=-3/4(1)+b. now solve.
2=-3/4+b
8/4+3/4=11/4
b=11/4
so, y=-3/4x+11/4