Write the equation of the graph below.

Answer:
-x²+8x-15
Step-by-step explanation:
There are two solutions: 3 and 5
First, let's write the equation in this form (pay attention, the parabola here is going up so it won't be like your graph):
(x-3)(x-5)
For resolve our problem, let's re-write it with a minus before:
-(x-3)(x-5)
You can also expand it and the result will be like this:
-x²+8x-15