Question: How to manipulate numeric DE solutions?

Also always i try to solve that strange ecuation maple give me like an aswer in terms of Z, with an integral on it, i don't get nothing. I evaluate a point with right click, evaluate a point. Choose the variables value, and the time at wich i want to evaluate the ecuation. Later it give me the same strange solution but with the variables replaced for the values i gave to the program. Then i choose right click, aproximate, and don't matter if i select 5, 10 or more digits, it launchs to me the same strange ecuation, not the number i'm waiting for.

So that i want to know now is how can i manipulate a numerical solution to a diff ecuation.

For example if i got this system of diff ecuation

dx/dt = (-k/m) (x srqt(x^2 + y^2))

dy/dt = (-k/m) (y srqt(x^2 + y^2)) - g

Which is a projectile trajectory taking care of air drag force, and i want to know at which initial speed i have to fire the body to reach 300m if it is fired from the initial point at (0,0), and it's initial velocity on x is 3 times it's initial velocity on y (initial launch angle condition)? 

How can i input that conditions to make maple give me a solution for something like that?