Hi,

I hope someone can help me determine the quadratic equation for the following word problem:

Note that below is question 1:

I was easily able to develop the equation for question 1, which the question prompt for a linear equation, as follows:

Now for question 2, I need to develop a quadratic equation which represents the pool being drained. I know that the vertex would be at (8,0) and that the quadratic equation format is y = a(x-h)^2+k, but I don't know where to go from there in terms of developing the equation for word problem. According to the textbook the equation is:

I understand the (x-8)^2 part, but not the value for "a", as in

Help would be greatly appreciated.