Help Bisection method Matlab

Hi! I have to write a code using the bisection method. The teacher said to double check it because there is a mistake, but it looks fine to me. Could you please help me to find out what's wrong? The exercise is attached

Here is my code

a = 0.22; b = 0.08; % dimensions of the spring system [m]
K1 = 1600; % first spring system coefficient [N/m]
K2 = 1e5; % second spring system coefficient [N/m3]
L0 = sqrt(a^2+b^2); % initial spring length [m]
L = @(x) sqrt(a^2+(b+x).^2); % deformed spring length [m]
u = @(x) L(x)-L0; % deformed distance [m]
Fs = @(x) K1.*u(x)+K2.*u(x).^3; % applied force to deform spring [N]
W = @(x) 2.*Fs(x).*(b+x)./L(x); % weight force to deform the system of springs [N]
x0 = 0; xn = 0.25; % x interval
X = linspace(x0,xn);
plot(X,W(X)) % mass W in the interval X
hold on
Q = 400; % applied force to the system [N]
n = 100; % number of iterations to define root
for i = 1:n % Bisection method for an applied force Q in an interval X
xm = (x0+xn)/2; % estimated solution, midpoint of the interval
if (W(x0)-Q)*(W(xm)-Q) < 0 % check of which subinterval contains the solution
xn = xm;
else
x0 = xm;
end
plot(xm,W(xm),'*r') % plot of each estimated solution
end

[Sam Chak]

If your teacher wants you to find the mistake, would you learn something if someone points out to you? What is the difference if your teacher points out the mistake to you?

These are rhetorical questions.

If you want some quick answers, you should at least explain what you did (explain the math) and what you want the community to check.

Are you suggesting that the community to check the Bi-section formula? Or the mechanics of the physics problem?

[ilaria scanu]

I was asking mainly about the bisection, I think the mechanics of the physics should be correct

[Torsten]

Except for that you should leave the bisection loop earlier than after 100 iterations (based on abs(W(xm)-Q) and abs(x0-xm)), I can't see anything wrong in your code.