First of all, I'm going to assume that we have a concave down parabola, because the stream of water is subjected to gravity.
If we need the vertex to be at
, the equation will contain a
term.
If we start with
we have a parabola, concave down, with vertex at
and a maximum of 0.
So, if we add 7, we will translate the function vertically up 7 units, so that the new maximum will be 
We have

Now we only have to fix the fact that this parabola doesn't land at
, because our parabola is too "narrow". We can work on that by multiplying the squared parenthesis by a certain coefficient: we want

such that:
Plugging these values gets us

As you can see in the attached figure, the parabola we get satisfies all the requests.
A. Frank has 24 marbles. I found this because Dan has 15 and total is 63 so subtract 63-15= 48. 48 divided by 2 people, which are Ellie ans Dan is 24. Dan has 24 marbles.
D'(-3,-4)
E'(-3,-10)
F'(3,-6)
Multiply 2x-2y=10 by 2,
4x-4y=20,
given:4x-5y=17
y=3
pluck it in
2x-6=10
move the 6 to the right
2x=16
divide
x=8
y=3