Question: solving system of ode

hi

i have written the following code but it not converge. how can i do?

> restart;
>
nn:=2;
Nt:=0.5;
NB:=0.5;
Le:=0.5;
Pr:=2;
b:=18;

 sol := dsolve({diff(G(x), x, x)+Le*f(x)*(diff(G(x), x))+(Nt/NB)*diff(T(x), x, x) = 0,diff(f(x), x, x, x)+f(x)*(diff(f(x), x, x))-(2*nn)/(nn+1)*(diff(f(x), x))^2 = 0,diff(T(x), x, x)/Pr+f(x)*(diff(T(x), x))+NB*(diff(T(x), x))*(diff(G(x), x))+Nt*(diff(T(x), x))^2=0,G(0) = 1, G(b) = 0, T(0) = 1, T(b) = 0, f(0) = 0, (D(f))(0) = 1, (D(f))(b) = 0}, numeric);



                               2
                              0.5
                              0.5
                              0.5
                               2
                               18
Error, (in dsolve/numeric/bvp) initial Newton iteration is not converging
>
plots[odeplot](sol,[x,T(x)],0..b,thickness=3,symbol=circle,style=point,symbolsize=13,color=black,numpoints=28);

thancks