Problem using the Secant Method

I want to solve a problem in which I am given a function (seen below) where W is 250 and I must find x. I have to use the secant method but I am having trouble with this as I only know how to find the roots. How can I do this?

% Function that determines the weight or downward force(W) of an object
% with a chosen vertical deflection value "x" in m.

function W = weight(x)
a = 0.15;                   %Constant value "a"
b = 0.05;                   %Constant value "b"
K = 2800;                   %Force of springs in N/m
L = sqrt(a^2+(b+x)^2);      %Hypotenuse Length of Right Triangle
Lo = sqrt(a^2+b^2);         %Unstretched Length
dL = L-Lo;                  %Difference of Stretched vs Unstretched Length
SINtheta = (b+x)/L;         %Length of side opposite angle theta/Hypotenuse
W = 2*K*dL*SINtheta;        %Downward force due to weight in N
end

Answer 1

[Star Strider]

I would add 250 to ‘W’ and solve for the root.

[Yianni]

On the second to last line?

[Star Strider]

Yes. That’s how I would do it.