Finding a parameter for a condition

Hi,

I first set a value for a my constant R. Based on this I determine different parameters. But in the end I want to know the value of R for a certain condition. This condition is Fb=Fg What kind of command can I use for this?

Thanks!

Code:

if true
  % code
r = 4.3;
R = 9.8;
Tp = 6.5;
A = pi^2*(R^2-r^2);
V = 0.25*pi^2*(R+r)*(R-r)^2;
rho_sea = 1025;
g = 9.81;
A_c1 = pi * r^2;
A_c2 = pi * R^2;
A_wp = A_c2 - A_c1;
c = rho_sea * g * A_wp;
r_pipe = (R-r)/2;
m_a =4*pi*rho_sea*r_pipe^2*R*[2/pi*log(8*R/r_pipe)+((3-4*log(2))/pi)];
f = 1/Tp;
omega = f*2*pi;
M = c/omega^2;
m_structure = M - m_a;
Fg = m_structure * g;
Fb = rho_sea * g * V/2;
r = 4.3;
R = 9.8;
Tp = 6.5;
A = pi^2*(R^2-r^2);
V = 0.25*pi^2*(R+r)*(R-r)^2;
rho_sea = 1025;
g = 9.81;
A_c1 = pi * r^2;
A_c2 = pi * R^2;
A_wp = A_c2 - A_c1;
c = rho_sea * g * A_wp;
r_pipe = (R-r)/2;
m_a =4*pi*rho_sea*r_pipe^2*R*[2/pi*log(8*R/r_pipe)+((3-4*log(2))/pi)];
f = 1/Tp;
omega = f*2*pi;
M = c/omega^2;
m_structure = M - m_a;
Fg = m_structure * g;
Fb = rho_sea * g * V/2;
end