Answer:
-2.5
Explanation:
For roots "a" and "b" a quadratic can be written as ...
(x -a)(x -b) = x^2 -(a+b)x +ab
Note that the coefficient of x is -(a+b), the opposite of the sum of the roots.
__
If we divide your equation by 2, we can put it into the form above:
x^2 -(-5/2)x -3/2 = 0
This tells us the sum of the roots is -5/2 = -2.5.