Answer: D. 16
Work Shown
-3 = -x^2 + 2x
-3+x^2-2x = 0
x^2 - 2x - 3 = 0
Compare this to the template ax^2+bx+c to find that
a = 1, b = -2, c = -3
Plug those values into the discriminant formula.
d = b^2 - 4ac
d = (-2)^2 - 4(1)(-3)
d = 4 + 12
d = 16 is the discriminant
The discriminant being a positive number means we have two unique solutions. Furthermore, the discriminant being a perfect square means the two solutions are rational.