Find the vertex:

Determine if the parabola will open up or down:

Since the value of a is positive, the parabola will open upwards
Find the x and y intercepts:
Factor
to find the x intercepts
(x+8)(x+2)
x + 8 = 0
x = -8
x + 2 = 0
x = -2
x intercepts:
x = -2
x = -8
Find the y intercept

Hence, C. Graph A best represents the quadratic function 
Answer:
Please restate your question.
It needs the y-intercept to be decipherable.
Step-by-step explanation:
Radius is half of the diameter so it's 7 for the diameter.