Question cb03a94d

Advanced Math - Nonlinear equations in one variable and systems of equations in two variables

In the $x y$ -plane, a line with equation $2 y = 4.5$ intersects a parabola at exactly one point. If the parabola has equation $y = - 4 x^{2} + b x$ , where $b$ is a positive constant, what is the value of $b$ ?