So, the equation I got was y = -7x -15.
Firstm you gotta find the slope using the slope formula, m = (y2-y1) / (x2-x1) (plug in the two initial points you were given, (7,-2) and (8,5). After you get the slope, which I got as -7, plug that into the y=mx+b formula with your last point (-3,6)
So, 6= -7(-3) + b //// -7 = m, -3 = x, 6 = y. after you solve the equation you should get -15. plug that into the y=mx+b formula andyou have your final equation,
y = -7x -15. to check if all of the point are on this equation, I'd recommend plugging the equation into the demos graphing calculator, it really helps. Hopefully this helped you!