Integrating 2nd order differential equation with ode45

I'm trying to complete this assignment but I am having trouble with my code and I'm not sure why. Here is my assignment

Here is my code I have written:

ti = 0;
tf = 10;
x0 = [1 0];
mass = 0;
b = 2.5;
k = 0;

for ii = 1:3
    mass = mass + 1;
    b = b-0.5;
    k = k+2;
    [time,position] = ode45(@(t_p2,x)odeMSD(t_p2,x,mass,b,k),[ti tf], x0);
    
    figure(2), hold on
    subplot(1,3,ii), hold on
    plot(time,position(:,1), 'm') , plot(time,position(:,2), 'k')
    legend('X Position (m)', 'Velocity (m/s)')
    xlabel('Time (s)')
end

subplot(1,3,1)
title('1st Parameter')

subplot(1,3,2)
title('2nd Parameter')

subplot(1,3,3)
title('3rd Parameter')

hold off

function xde = odeMSD(t_p2,x,m,b,k)
    xde = zeros(2,1);
    xde(1) = x(1);
    xde(3) = -(b./m).*x(2) - (k./m)*x(1);
end

Answer 1

[madhan ravi]

    xde(2) = -(b./m).*x(2) - (k./m)*x(1);
        ^----------should be 2 not 3!

[Ryan Bowman]

Thank you!! I think also my initial conditions might be entered in wrong. Is this true?

[madhan ravi]

Anytime :) , yes it should be

x0 = [1 1];
        ^----should be 1