(1/2,3)(2,3/4)
slope = (3/4 - 3) / (2 - 1/2) = (3/4 - 12/4) / (4/2 - 1/2) =
(-9/4) / (3/2) = -9/4 * 2/3 = -18/12 = -3/2
Answer: None
Step-by-step explanation: They are parallel and would never intersect
Whenever you face the problem that deals with maxima or minima you should keep in mind that minima/maxima of a function is always a point where it's derivative is equal to zero.
To solve your problem we first need to find an equation of net benefits. Net benefits are expressed as a difference between total benefits and total cost. We can denote this function with B(y).
B(y)=b-c
B(y)=100y-18y²
Now that we have a net benefits function we need find it's derivate with respect to y.

Now we must find at which point this function is equal to zero.
0=100-36y
36y=100
y=2.8
Now that we know at which point our function reaches maxima we just plug that number back into our equation for net benefits and we get our answer.
B(2.8)=100(2.8)-18(2.8)²=138.88≈139.
One thing that always helps is to have your function graphed. It will give you a good insight into how your function behaves and allow you to identify minima/maxima points.
Cos(theta) = adjacent/hypotenuse
cos(theta) = 6/20
cos(theta) = 0.3
Use the inverse cos or cos^-1 on your calculator to get the angle
theta = 72.5