The speed of water can be split into vertical and horizontal speed components:

Due to the force of gravity, the y component will be parabolic. The x component will be linear:

To find when the water hits the ground 2.5m away, set y= 0 and x = 2.5
Earths atmosphere, Temperature, Plant life and Oxygen I guess
Without a change in pressure
V/T = V/T
Before change = after change - expansion
x = volume at m3
(0.5)/20 = x/45
.025 = x/45
.025 * 45 = x
1 = x
The volume of this gas is 1 m3.
Hope this helps :) also the gas expanded .5 of m3.