This is a quant comparision question from Math Fundamentals/Basics Quiz #2: Level 3

given equation:

6x^2 + 3x = 30

A: The sum of all valid x values

B: 0

The answer key has answer: B. How though?

When you solve for x you get -2 and 5/2.

Their sum gives 1/2. The answer should be A right? Or am I missing something?