I have got help from Damon on this question but all I need is help on integrating the answer he gave me into my original equation:

y=-15/20.25(x+1.5)^2+0

Here's Damon's help: (x+1.5)(x+1.5) = x^2 + 1.5 x + 1.5 x + (1.5*1.5)

= x^2 + 3 x + 2.25

So how would I put this into my original quadratic equation?

Please and thank you as the help would be much appreciated!

You started out wanting to simplify

y=-15/20.25(x+1.5)^2+0
y=a(x+2)^2+1.5

I assume that means

y = -15/20.25 (x+1.5)^2
-15/20.5 (x^2+3x+2.25) = -0.73x^2 - 2.20x - 1.65

Not sure that's any simpler than what you started out with.

As for the second, you cannot find a value for a, without knowing something else about the function. It's just a parabola with vertex at (-2,1.5) and there are lots of those.