I would suggest you a solution,
Since you have known two points of slope, which are (40,35) and (74.4, 15), you can easily get a segment passing to these points. Let say, y = ax + b.
Then, you can define a function, for example phi(x,y) = ax + b - y. As it can seen that phi(x,y) > 0 if (x,y) is in the left of the slope and phi(x,y) < 0 if (x,y) is in the right of the slope and phi(x,y) = 0 if (x,y) is in the slope. This technique is called "levelset method".
Now, what you can do is to use the phi funtion to check a point is in the left or the right of the slope. If it is in the right, you just eleminate it.