how can i solve this proplem by rung-kutta method ?

this is my sol form

x = linspace(0,1,20);

t = linspace(0,2,5);

function [c,f,s] = pdex1pde(x,t,T,DuDx);

c = 1;

f = DTDx-4;

s = 0;

end;

function u0 = pdex1ic(x)

u0 = 0;

end;

function [pl,ql;pr;qr] = pdex1bc(xl,ul,xr,ur,t);

T0 = 418.5;

pl = Tl;

ql = 0;

pr = 1;

qr = 1;

end;

m = 1;

sol = pdepe(m,@pdex1pde,@pdex1ic,@pdex1bc,x,t);

u = sol(:,:,1);

surf(x,t,T);

title('Numerical solution computed with 20 mesh points');

xlabel('شDistance x');

ylabel('Time t');

figure;

plot(x,T(end,:));

title('Solution at t = 2');

xlabel('Distance x');

ylabel('T(x,2)');