Equation :
This parabola is facing downwards and highest point of the parabola is it's vertex.
Highest point is (-2,2)
so the vertex is (-2,2)
The graph is passing through (-1,0)
Equation in vertex form is


Substitute back in Equation

the graph has two x intercepts -1 and -3
that means (x+1) and (x+3) are the factors
multiply factors to get the equation in standard form

-2x^2-8x-6=0