6.3 should be the correct answer.
So, we are given the y intercept, and since we know c is the same as the y value of the y intercept, we know that c=15.
From there we can pick any two of the points given to us to find our a and b.
Let's use (4,17) and (8,23) becase they are whole numbers.

So, with b=0, we can plug it back into the first equation to get:
So our quadratic is 
Answer:
y is greater than or equal to 0.5/2.5x-1/2
y is greater than -2x
Step-by-step explanation:
All angles in an equilateral triangle are 60°, so you can use trigonometry and say that
sin(60) = 46/side
side = 46/sin(60)
side = 46/0.866 = 53.12. I hope this helps!