Solving nonlinear equation using newton-raphson method

Hello, I have this code that is wrong. I want to solve an equation (f) using newton's method. I want to update my old V value to the eqation for f and df, but I just can't get my head wrapped around it. Could anyone help please?

NB: The answer should be 0.86728 assuming the initial value of V is 0.

P=6;
T=2;
N = 500;
tol = 0.0001;
V = zeros(1,N);
f = zeros(1,N);
df = zeros(1,N);
del = 0;
Vnew = 0;

while del < tol 
    for i = 2:N
        V(i) = Vnew;
        f(i) = 3*P*V(i).^3 - P*V(i).^2 + 9*V(i) - 8*T*V(i).^2 - 3;
        df(i) = 9*P*V(i).^2 - 2*P*V(i) - 16*T*V(i) + 9;
        Vnew = V(i-1) - (f(i)/df(i));
    end
    del = V(i) - V(i-1);
end

Answer 1

[Matt J]

i=0; del = Inf; 
while del > tol && i<N 
   
        i=i+1;
        
        f(i) = 3*P*V(i).^3 - P*V(i).^2 + 9*V(i) - 8*T*V(i).^2 - 3;
        df(i) = 9*P*V(i).^2 - 2*P*V(i) - 16*T*V(i) + 9;
        V(i+1) = V(i) - (f(i)/df(i));
        

        del = abs(V(i+1) - V(i));
end

lastValue = V(i+1),