Try making a grid like this. Apologies for the terrible drawing and handwriting. It represents all possible results of rolling two dice and summing their values. The blue column and yellow row represent the values of each die, and the green numbers reptesent their sums.
First, you can see that there are 36 possible values. Second, it's easy to see how many results are greater than 9, since they're all in one corner. And last, you can see just how many are even and how many are odd. Remember to reduce your fractions in the end.
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.
You can check your factoring by multiplying them all out to see if you get the original expression. If you do, your factoring is correct; otherwise, you might want to try again