This question is relatively simple to answer if we ignore air resistance. But actually in this case it will be a very rough estimate, because such a great initial speed means huge air resistance.
I hope this is a sample problem about a free fall and that you don't need to use the result in practice.
The simplest method to find the maximum height, denote it `H_1,` is to consider energy (also denote the initial speed as `V_0`). If we measure potential energy off of the ground level, then at the start a bullet has only kinetic energy `(m*V_0^2)/2.` At the maximum height, when a bullet starts to fall, the speed will be zero, and a bullet has only potential energy `m*g*H_1.`
Because of energy conservation `(m*V_0^2)/2=m*g*H_1,` so
`H_1=(V_0)^2/(2g) approx (450)^2/20` =10125 (m). This is the formal answer. In reality it will be much less, when taking air resistance into consideration.