Answer
$112.5\;\rm nm$, $225\;\rm nm$
Work Step by Step
As we see in the figure below, the second ray (ray 2) reflects with $\pi$-phase change.
We have here two cases, when the glass appears bright and when the glass appears dark when we use the same light of $450\;\rm nm$ wavelength.
We need to have a constructive interference with the two reflected rays when the thickness of the air film is minimum we can use to got that.
The two reflected rays are out of phase, so the path length difference of must be half a wavelength, so both rays will met with the same phase.
$$2t=\dfrac{\lambda}{2}$$
Thus,
$$t=\dfrac{\lambda}{4}$$
Plugging the known;
$$t=\dfrac{450}{4}=\color{red}{\bf 112.5}\;\rm nm$$
And when we need a constructive interference, the path length difference must be equal to one wavelength, so both of the two rays will met out of phase.
$$2t=\lambda$$
$$t=\dfrac{\lambda}{2}=\dfrac{459}{2}=\color{red}{\bf 225}\;\rm nm$$
