How do i solve this equations?

Hi, i'm working on a model for a water rocket launch. But i'm struggling to get the drag and velocity formula's time related. The drag depends on the velocity and the velocity on the drag. Does anyone know how i can solve this?

P = 400000;                       %pressure difference (MpA)
rhow = 999.1026;                  %density of water (kg/m^3)
rhoa = 1.2922;                    %density of air (kg/m^3)
Cd = 0.4;                         %coefficient of drag 
An = 0.0003801327111;             %nozzle area (m^2)
As = 0.003848;                    %surface area rocket (m^2)
Mempty = 0.067;                   %empty mass of the rocket (kg)
Mwater = 0.350;                   %mass of the added water (kg)
Mfull = Mempty+Mwater;            %mass of the rocket full (kg)
g = 9.81;                         %gravitational constant (m/s^2)
K = 0.4;                          %k-loss factor
Ta = 0.0238;                      %time of acceleration (s)

deltaP = 0.5*rhow*(29.8^2)*K;     %minor losses of pressure in nozzle
Ve = 2*sqrt((P-deltaP)/rhow);     %exit velocity of the propellant (m/s)
Mf = rhow*Ve*An;                  %mass flow of the propellant (kg/s)
Fthrust = Ve*Mf;                  %thrust generated by mass flow of propellant (N)
athrust = Fthrust/Mfull;          %acceleration due to thrust force (m/s^2)
Ta = Mwater/Mf;                   %time of acceleration (s)
Vmax = (athrust-g)*Ta;            %maximum velocity achieved (m/s)
H1 = ((athrust-g)/2)*Ta^2;        %height achieved after acceleration (m)

Fd = -0.5*Cd*As*rhoa*V^2;         %drag force (N)
adrag = Fd/Mempty;                %decelleration due to drag (m/s^2)

V = Vmax -g*(t-Ta)+adrag*(t-Ta);                          %flight trajectory velocity (m/s)
H = Vmax*(t-Ta) -0.5*g*(t-Ta)^(2) + 0.5*adrag*(t-Ta)^(2);

[Jyotish Robin]

In the above code, you are using 'V' to calculate 'adrag' and 'adrag' to calculate 'V'. This will obviously lead to problems.

>>Fd = -0.5*Cd*As*rhoa*V^2;

This will throw an error since 'V' is not defined.

Also in your code, the variable 't' is not defined. You can use something similar to below code to define 't'.

 >>t=0:.01:100

Hope the above suggestions help!