Solve Second Order ODE Numerically

I am having trouble solving this second order ODE using MATLAB. We are supposed to use the secant iteration method or runge-kutta method, or numerical method. I dont know where to begin besides what I have here.

A target is 1200 meters away. A ball is launched with an initial velocity of 150m/s with unknown angle. Air resistance is involved. Find the angle the ball was launched at. b is the constant for air resistance, and the other parameters are given below.

clear all;

%initial conditions

%vo*cos(theta)=vx(0)

%vo*sin(theta)=vy(0)

%Equation of motion with friction

% m(d/dt)^2(vx)=-b*sqrt(vx^2 + vy^2)

% m(d/dt)^2(vy)=-b*vo*sin(theta)-m*g

xf=1200

vo=150

b=(.5)*(.009)*1.2*.5

g=-9.8

m=5