so we have the points of (0,-7),(7,-14),(-3,-19), let's plug those in the y = ax² + bx + c form, since we have three points, we'll plug each one once, thus a system of three variables, and then we'll solve it by substitution.
well, from the 1st equation, we know what "c" is already, so let's just plug that in the 2nd equation and solve for "b".
well, now let's plug that "b" into our 3rd equation and solve for "a".