Re-evaluating, the standard form $ y = -ax^2 + bx + c $ with vertex $ (3, 10) $ gives $ b = 2a \cdot 3 = 6a $ and $ 10 = -a(9) + b(3) + c $. Substituting $ b = 6a $ and $ c = 4 $ (from $ (0, 4) $):