13/2 = 6.5
2/13 = 015
6.5-0.15 = 6.35
<em>I would say that your answer is </em><em>44</em>
Assume the parabola is placed on a graph where the x-axis is the top of the dish.
The vertex is then at (0,-30) The x-intercepts or zeros are at (-30,0) and (30,0)
The equation of such parabola would be:

Plug in vertex to find value of 'a'

Now find the focus given that


Answer: the microphone should be placed 7.5 inches from vertex.
X^2 + 4x = 0
x^2 + 4x + 4 = 0 + 4
(x + 2)^2 = 4