Choice A is the correct answer. We only need the x-coordinate, given by $x = -b/2a$.

1. $a = 5$, $b = -20$.
2. $x = -(-20) / (2 \times 5)$.
3. $x = 20 / 10 = 2$.

Choice B is incorrect because of a sign error. Choice C is incorrect because it forgets to multiply $a$ by 2. Choice D is incorrect because it uses $a$.