Question

Solve −2x2 +3x − 9 = 0.

Answer 1

Always do the multiplication first
Followed by division , plus then minus.

Answer 2

x= 3
x= 3/2

Start by separating your equation a little more. 
(-2x+3)(x-3)=0
Set each of those binomials equal to zero.
-2x+3 = 0
x-3 = 0
And solve
-2x = -3
-3/-2 = 3/2
x= 3