Since the x value of the vertex is -b/2a in ax^2+bx+c, we have -3 as b and -1 and a, getting -(-3/-1*2)=-(3/2)=-3/2 as the x value of the vertex. To get the y value of the vertex, we plug the x value of the vertex into the function, resulting in -(3/2)^2-3*(-3/2)+6=8.25, making the vertex (-3/2, 8.25)