Nope. That is wrong. Why you choose t = 19s?
You know the plane is 1237 m above the ground, when the package is dropped.
The package will reach its maximum height when its velocity is 0. Because the package's initial velocity is 28 m / s. And it decelerates to 0 m / s. After that it will start to fall down. So when the package's velocity is 0, it reaches its max height.
How long does it take for the package to decelerate to 0 m / s?